Plasma processing method and plasma processing apparatus

ABSTRACT

In a plasma processing method for processing an object which is placed in a reactor container, by decomposing a raw material gas in the reactor container using a high frequency power outputted from a high power supply and introduced into the reactor container via a matching device and an electrode, the adjustment of impedance by the matching device during plasma processing is controlled within a predetermined impedance variable range, and the impedance variable range is changed as plasma processing proceeds. Another plasma processing method employing a plurality of power supply systems having high frequency power supplies and matching devices capable of changing impedances and controlling the adjustment of impedance by at least one of the matching devices during plasma processing within a predetermined impedance variable range. A plasma processing apparatus using a plurality of power supply systems having matching circuits capable of changing impedances and control systems for controlling the impedances of the matching circuits, and the control system is capable of storing a variable range setting value for limiting an impedance variable range.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a plasma processing method and aplasma processing apparatus using the high frequency power for use information of a deposition film and etching in a semiconductor device, anelectrophotographic photosensitive member, a line sensor for imageinput, a photographing device, a photovoltaic device or the like, or foruse in cleaning and the like in a plasma processing apparatus afterformation of a deposition film.

[0003] 2. Related Background Art

[0004] Conventionally, as a deposition film formation process used toproduce a semiconductor device, an electrophotographic photosensitivemember, a line sensor for image input, a photographing device, aphotovoltaic device, or other electronic or optical element, many typesof methods have been known, such as vacuum deposition, sputtering, ionplating, thermal CVD (Chemical Vapor Deposition), photo-assisted CVD andplasma CVD, and apparatuses for the methods have been put to practicaluse.

[0005] Among them, a plasma CVD method, which provides a thin depositionfilm formed on a substrate by using a direct current, high-frequency, ormicrowave glow discharge to decompose a raw material gas, is nowincreasingly put to practical use as a suitable measure for forming adeposition film of amorphous silicon hydride (hereinafter referred to as“a-Si:H”) for electrophotograph, and various kinds of apparatus used forthe method have been proposed.

[0006] In addition, among plasma CVD processes, VHF plasma CVD(abbreviated as “VHF-PCVD” hereinafter) using the VHF-band highfrequency power has attracted attention in recent years, and developmentfor formation of various kinds of deposition films using this process isbeing vigorously conducted. This is because VHF-PCVD enables a film tobe deposited at high speed and provides a high quality deposition film,and is thus looked upon as a process capable of achieving reduction incosts and enhancement of quality of products at the same time. Forexample, Japanese Patent Application Laid-Open No. 6-287760(corresponding to U.S. Pat. No. 5,534,070) discloses an apparatus and amethod that can be used for forming an amorphous silicon (a-Si) basedlight-receiving member for electrophotography. Also, plasma processingapparatuses as shown in FIGS. 4A and 4B and FIGS. 6A and 6B, which canform a plurality of light-receiving members for electrophotography atthe same time and thus achieve very high productivity, are underdevelopment.

[0007]FIG. 4A is a schematic sectional view of a conventional plasmaprocessing apparatus, and FIG. 4B is a schematic sectional view takenalong a cutting plane line 4B-4B of FIG. 4A. An exhaust pipe 411 isprovided on the side face of a reactor container 401 as one united body,and the other end of the exhaust pipe 411 is connected to an exhaustingsystem (not shown). Six cylindrical substrates 405 on which depositionfilms are to be formed are disposed in parallel to one another in such amanner as to surround the central portion of the reactor container 401.Each cylindrical substrate 405 is supported by a rotation shaft 408, andis heated by a heating element 407. When a motor 409 is driven, therotation shaft 408 is rotated via a reduction gear 410, and thecylindrical substrate 405 is rotated around the central axis in thegeneratrix line direction thereof (central axis along the lengthwisedirection of the cylindrical substrate).

[0008] A raw material gas is supplied to a film formation space 406surrounded by six cylindrical substrates 405 from raw material gassupplying means 412. The VHF power that is a high frequency power issupplied to the film formation space 406 from a high frequency powersupply 403 through a matching device (hereinafter referred to as amatching box) 404 and then a cathode 402. At this time, the cylindricalsubstrate 405 kept at a ground potential through the rotation shaft 408serves as an anodic electrode.

[0009] Formation of deposition films using such an apparatus cangenerally be performed according to the procedure described below.

[0010] First, the cylindrical substrates 405 are installed in thereactor container 401, and gas is exhausted from the reactor container401 by an exhausting system (not shown) via the exhaust pipe 411.Subsequently, the cylindrical substrates 405 are heated by the heatingelement 407 while control is performed so that they are kept at apredetermined temperature of about 200 to 300° C.

[0011] When the temperature of the cylindrical substrate 405 reaches apredetermined temperature, the raw material gas is introduced into thereactor container 401 through the raw material gas supplying means 412.Also, after it is checked that the pressure in the reactor container 401is stabilized, and the output of the high frequency power supply 403 isset at a predetermined value. Subsequently, the impedance of a matchingcircuit in the matching box 404 is adjusted so that the output impedanceof the high frequency power supply 403 equals the impedance of the inletof the matching box 404. In this way, the VHF power that is a highfrequency power is efficiently supplied to the reactor container 401through the high frequency electrode 402, a glow discharge is producedin the film formation space 406 surrounded by the cylindrical substrates405, and the raw material gas is excited and dissociated to form adeposition film on the cylindrical substrates 405.

[0012] After a film having a desired thickness is formed, supply of VHFpower is stopped, and subsequently supply of the raw material gas isstopped to complete the forming of the deposition film. By repeating thesame operation several times, a desired multilayered light-receivinglayer of multi-layer structure can be formed.

[0013] During formation of the deposition film, the cylindricalsubstrate 405 is rotated at a predetermined speed with the motor 409 viathe rotation shaft 408 to form the deposition film over the entiresurface of the cylindrical substrate.

[0014] In this formation of a deposition film, the impedance adjustmentof the matching circuit in the matching box 404 is performed manually orautomatically. In the case of automatic adjustment, the matching box 404comprises therein a system including a matching circuit 501 and acontrol system 500. The matching circuit 501 is constituted of amatching variable condenser 502, a tuning variable condenser 503 and acoil 504, and at the inlet of the matching circuit 501, a high frequencycurrent is detected by a current detection element 505, and a highfrequency voltage is detected by a voltage detection element 506. Theoutputs of the current detection element 505 and the voltage detectionelement 506 are inputted in a phase difference detector 507 and animpedance detector 508 in the control system 500. In the phasedifference detector 507, the phase of impedance at the inlet of thematching circuit 501 is detected, and a voltage consistent with thephase of impedance is outputted to a tuning control circuit 509. In thetuning control circuit 509, the voltage inputted from the phasedifference detector 507 is compared with a reference voltage, and avoltage consistent with the difference therebetween is supplied to amotor 510 for driving the tuning variable condenser 503. As a result,the tuning variable condenser 503 is adjusted by the motor 510 so thatthe phase of impedance satisfies a predetermined matching goalcondition, for example, the phase equals 0. On the other hand, in theimpedance detector 508, the absolute value of impedance at the inlet ofthe matching circuit 501 is detected, and a voltage consistent with theabsolute value of impedance is outputted to a matching control circuit511. In the matching control circuit 511, the voltage inputted from theimpedance detector 508 is compared with the reference voltage, and avoltage consistent with the difference therebetween is supplied to amotor 512 for driving the matching variable condenser 502. As a result,the matching variable condenser 502 Is adjusted by the motor 512 so thatthe absolute value of impedance satisfies a predetermined matching goalcondition, for example, the absolute value of impedance equals 50 Ω. Inthis configuration, the impedance adjustment is automatically performed,and thus the high frequency power is efficiently supplied to the reactorcontainer 501.

[0015] For further improving vacuum processing characteristics, atechnique is under development in which a plurality of powers ofdifferent frequencies are supplied to the reactor container at the sametime. For example, Japanese Patent Application Laid-Open No. 11-191554discloses a technique in which a first high frequency power having afrequency of 300 MHz to 1,000 MHz and a second high frequency powerhaving a frequency of 50 kHz to 30 MHz are supplied to the sameelectrode at the sane time, and this technique reportedly allows activespecie control effects to be enhanced, thus making it possible to carryout accurate plasma processing. Also, Japanese Patent ApplicationLaid-Open No. 7-74159 discloses a technique in which a 60 MHz highfrequency power and a 400 kHz low frequency power are supplied to thesame electrode with one power superimposed on the other, and thistechnique reportedly enables a self bias to be controlled stably, thusmaking it possible to improve an etching rate and curb the occurrence ofparticles.

[0016] For supplying a plurality of high frequency powers to the reactorcontainer, an independent matching device is provided in each highfrequency power supply system to adjust the impedance of the matchingdevice for each high frequency power supply system, whereby the highfrequency power is supplied to the reactor container efficiently.Specifically, impedance adjustment is carried out in the same way as thecase where a single high frequency power is supplied.

[0017] In this way, the vacuum processing method in which a plurality ofpowers of different frequencies are supplied to the reactor container atthe same time provide a variety of actions depending on influences ofemployed frequencies and power ratios or specific procedures of vacuumprocessing, and it is expected that those actions will play an importantrole to improve the vacuum processing characteristics by using thoseactions effectively.

[0018]FIGS. 6A and 6B are schematic diagrams of a plasma processingapparatus capable of supplying a plurality of high frequency powers ofdifferent frequencies to the reactor container at the same time asdescribed above. FIG. 6A is a longitudinal sectional view of the plasmaprocessing apparatus, and FIG. 6B is a transverse sectional view takenalong the 6B-6B line in FIG. 6A.

[0019] An exhaust pipe 611 is provided in the lower part of a reactorcontainer 601 included in this plasma processing apparatus, and theother end of this exhaust pipe 611 is connected to an exhausting system(not shown). In this reactor container 601, six cylindrical substrates605 on which a deposition film is to be formed are placed in parallel toone another in such a manner as to surround the central portion. Eachcylindrical substrate 605 is supported on a rotation shaft 608, and isheated by a heating element 607. When a motor (not shown) is driven, therotation shaft 608 is rotated via a gear (not shown), and thecylindrical substrates 605 are thereby rotated around the central axisin the generatrix line direction thereof (central axis along thelengthwise direction of the cylindrical substrate).

[0020] A raw material gas is supplied from a raw material gas supplypipe 612 to a reactor container 601. A high frequency power is suppliedfrom a first high frequency power supply 603 through a first matchingbox 604 and then an internal high frequency electrode 602 to the reactorcontainer 601, and is also supplied from a second high frequency powersupply 615 through a second matching box 616 and thee an external highfrequency electrode 614 to the reactor container 601.

[0021] The method of forming a deposition film using this plasmaprocessing apparatus is generally carried out according to the proceduredescribed below.

[0022] First, the cylindrical substrates 605 are installed in thereactor container 601, and gas in the reactor container 601 is exhaustedby the exhausting system (not shown) via the exhaust pipe 611.Subsequently, the cylindrical substrates 605 are heated by a heatingelement 607 while control is performed so that they are kept at apredetermined temperature of about 200 to 300° C.

[0023] When the cylindrical substrates 605 are heated to a predeterminedtemperature, the raw material gas is introduced into the reactorcontainer 601 via the raw material gas supply pipe 612. After the flowrate of the raw material gas reaches a preset rate, and the pressure inthe reactor container 601 is stabilized, the output of the first highfrequency power supply 603 is set at a predetermined value, and at thesame time, the output of the second high frequency power supply 615 isset at a predetermined value. Subsequently, the impedance of thematching circuit in the first matching box 604 is adjusted so that theoutput impedance of the first high frequency power supply 603 equals theimpedance at the inlet of the first matching box 604. At the same time,the impedance of the matching circuit in the second matching box 616 isadjusted so that the output impedance of the second high frequency powersupply 615 equals the impedance at the inlet of the second matching box616.

[0024] In this way, the high frequency power is efficiently supplied tothe reactor container 601 via the internal high frequency electrode 602and the external high frequency electrode 614, and thus a glow dischargeis produced in the reactor container 601, whereby the raw material gasis excited and dissociated to form a deposition film on the cylindricalsubstrate 605.

[0025] After a deposition film having a desired thickness is formed, thesupply of high frequency power is stopped, and subsequently the supplyof the raw material gas is stopped to complete the forming of thedeposition film. By repeating the same operation several times, adesired multilayered light-receiving layer of multi-layer structure canbe formed.

[0026] During formation of the deposition film, the cylindricalsubstrate 605 is rotated at a predetermined speed with the motor via therotation shaft 608 to uniformly form the deposition film over the entiresurface of the cylindrical substrate 605.

[0027] The above-described methods and apparatus can realize gooddeposition film formation. However, the level of demands in the marketon products produced using such plasma processing are being raised dayby day, and for satisfying the demands, there is a need for a plasmaprocessing method and apparatus to produce a product with higherquality.

[0028] For example, for the electrophotographic photosensitive member,an enhanced copy speed, enhanced image quality and a reduced price arequite highly demanded, and in order to realize these, enhancement ofphotosensitive member characteristics, specifically, electrificationcapability, sensitivity or the like, and reduction in costs forproducing photosensitive members have become essential. Besides, withdigital electrophotographic apparatus or color electrophotographicapparatus, which have remarkably become widespread recently, copies ofphotographs, pictures, design drawings or the like, as well as scriptsare frequently made, and it is therefore required more strongly toreduce optical memory of the photosensitive member and to reduceunevenness of image density.

[0029] For achieving the improvement of plasma processingcharacteristics and reduction in costs for plasma processing, atechnique enabling the plasma having desired properties to be producedand maintained with stability and good reproducibility has becomeimportant. For example, f or plasma processing using a conventionalplasma processing apparatus shown in FIGS. 4A and 4B, the impedance inthe matching box is generally adjusted automatically in terms of laborsaving. In the conventional method of adjusting the impedance asdescribed above, however, proper control is not necessarily performed,for example, if the load impedance is temporarily changed due toabnormal discharge such as sparks.

[0030] Because the abnormal discharge itself is transient in most cases,and it often occurs in such a place that materials to be treated are notadversely influenced, so that the plasma processing may be preventedfrom being adversely influenced directly by the abnormal discharge. Inthe conventional method of adjusting the impedance, however, there arecases where when abnormal discharge occurs, the impedance of thematching box is adjusted so as to obtain matching with the loadimpedance in the abnormal state, and consequently an impedanceconsiderably deviated from a normal matching condition is set. As aresult, the normal impedance cannot be recovered immediately after theabnormal discharge is eliminated, which may lower plasma processingcharacteristics themselves and impair the stability of plasma processingcharacteristics. There are also cases where the impedance of thematching box is considerably changed when the abnormal discharge occurs,and thereby the abnormal discharge is further developed, thus making itimpossible to recover the normal plasma condition. In this way, in theconventional method of adjusting the impedance, an adequate measure tocounter a sudden change in load impedance caused by an abnormaldischarge or the like is not necessarily provided.

[0031] For the technique aiming at the adjustment of impedance, forexample, Japanese Patent Application Laid-Open No. 09-260096 discloses atechnique for automatically searching a matching point of impedance inwhich a matching point of an impedance with which plasma is ignited issearched using a preset impedance as a reference to ignite the plasma,and then a matching point of the preset impedance used as a referencefor providing stable plasma discharge is automatically reached, followedby stabilizing the plasma discharge using the matching point as areference, wherein plasma can reliably be ignited even if the loadimpedance is varied with plasma processing.

[0032] According to this technique, troubles during production ofplasma, for example, problems such that plasma is unignited for a longtime and so on are solved, but the above-described problems occurringafter a discharge is brought about, for example, problems in the casewhere an abnormal discharge occurs have not been solved yet.

[0033] Also, Japanese Patent Application Laid-Open No. 11-087097(corresponding to U.S. Pat. No. 5,936,481) discloses a techniquedirected to matching of impedance and power control systems, in whichthe impedance of each element in the matching circuit is fixed at apredetermined value for the matching of impedance, and the adjustment ofimpedance is carried out with the frequency of high frequency powerbeing changed. According to this technique, because the adjustment ofimpedance can be performed with an electrical process such that thefrequency of high frequency power is changed, the impedance is quicklyadjusted. In the case of this technique, however, according to the studymade by the inventors, if an abnormal discharge occurs during plasmaprocessing, and the load impedance is abruptly changed, matching isimmediately provided in correspondence to the impedance, and thus theabnormal discharge may be promoted. Also, in the case of this matchingof impedance with the frequency of high frequency power being changed,the frequency is varied for each process lot, and as a result there maybe variations between plasma processing characteristics. Thesevariations are significant especially when the frequency of highfrequency power is sensitive to the uniformity of plasma processingcharacteristics as in the frequency of high frequency power that is inthe VHF band.

[0034] Japanese Patent Application Laid-Open No. 08-096992 discloses atechnique in which the impedance is adjusted in the early stage of eachstep in plasma processing, no impedance adjustment is thereafter carriedout in the step, and the impedance adjustment is started again in thenext step, followed by maintaining the same conditions, wherein specifictiming for adjustment of impedance includes (1) a short time period foradjustment in the early stage of each step and (2) the time thatreflection is abnormally increased. This technique reportedly eliminatesthe inappropriate adjustment of impedance occurring when the highfrequency power is supplied from a plurality of electrodes, thus makingit possible to prevent the plasma from being destabilized. When thistechnique is used, no impedance adjustment is carried out even if theabnormal discharge occurs, and the abnormal discharge is prevented frombeing promoted. In the case of this technique, however, a change inimpedance over time during plasma processing is not dealt with, andmismatching of impedance is caused by, for example, a change in loadimpedance during the early stage of plasma processing, or a differencebetween the impedance in the early stage of processing and the impedanceimmediately before the processing is ended in long plasma processing.

[0035] Consequently, there are cases where adequate plasma processingproperties cannot be obtained due to this mismatching. Also, since thelevel of the mismatching varies depending on the condition of thereactor container, the plasma processing characteristic may be differentfor each plasma processing lot.

[0036] In addition, in the plasma processing method in which a pluralityof high frequency powers, especially a plurality of high frequencypowers of different frequencies are supplied to the reactor container atthe same time, significant effects can be obtained, but control ofplasma is difficult, and in present situation, there is a need for avariety of improvements in producing plasma having desiredcharacteristics with stability and good reproducibility.

[0037] When a plurality of high frequency powers are supplied to thereactor container at the same time, and particularly the plurality ofhigh frequency powers have different frequencies, the high frequencypowers interfere with one another. Therefore, in the conventional methodof adjusting the impedance as described above, there are cases whereaccurate adjustment of impedance cannot be carried out due tointerference of the plurality of high frequency powers.

[0038] For example, in the case where the first high frequency power andthe second high frequency power are supplied to the reactor container atthe same time, the first high frequency power propagates through thereactor container into the power supply system for the second highfrequency power. As a result, it appears as if the first high frequencypower that should not exist originally were existing as a reflected wavein the power supply system for the second high frequency power, and thusthere may arise a phenomenon in which the outputs of a power meter, aphase detector and an impedance detector do not reflect accuratelymatching conditions. Also, a similar phenomenon may occur in the powersupply system for the first high frequency power, thus making itimpossible to correctly keep track of matching conditions.

[0039] In this situation, the level of influence varies depending on theconditions of the power outputted from the other power supply system,namely the value of power, its phase and the like. Therefore, althoughthe condition of one power supply system is kept constant, for example,it appears as if load conditions changed when the condition of the otherpower supply system is changed, namely, the impedance of the matchingdevice is changed, so that inappropriate impedance adjustment would becarried out in spite of the fact that there is no change in matchingconditions. As a result, in some cases, impedance considerably deviatedfrom a real matching point is provided, causing the plasma to bedestabilized.

[0040] As a measure to counter these problems, a high pass filter and alow pass filter are generally installed in each power supply system.However, in this measure using filters, some degree of effect can beobtained, but it is difficult to completely inhibit the diffraction ofpower, and some influence by interference often remains. Particularly,when a plurality of powers of relatively close frequencies is used, itis generally quite difficult to adequately inhibit the diffraction ofthe other high frequency power even if filters are installed.

[0041] For example, when using the plasma processing apparatus shown inFIGS. 6A and 6B, a control system having such a configuration as shownin FIG. 5 is used as the control system provided in the matching boxes604 and 616 to carry out vacuum processing, the following phenomenon mayoccur.

[0042] For producing plasma in the reactor container 601, the rawmaterial gas is introduced into the reactor container 601 via the rawmaterial gas supply pipe 612, and thereafter the outputs of the firsthigh frequency power 603 and the second high frequency power 615 are setat predetermined values, respectively, followed by adjusting theimpedances of the matching circuits in the first matching box 604 andthe second matching box 616. Specifically, in the first matching box 604and the second matching box 616, the phase of impedance at the inlet ofthe matching circuit 501 is detected by the phase difference detector507, and then a voltage consistent with the phase of impedance isoutputted to the tuning control circuit 509.

[0043] The tuning control circuit 509 compares the voltage inputted fromthe phase difference detector 507 with a reference voltage, and thensupplies a voltage consistent with the difference therebetween to themotor 510 for driving the tuning variable condenser 503. The tuningvariable condenser 603. Is adjusted by the motor 510 so that the phaseof impedance consequently equals a predetermined value, generally “0.”At the same time, the impedance detector 508 detects an absolute valueof impedance at the inlet of the matching circuit 501, and then outputsa voltage consistent with the absolute value of impedance to thematching control circuit 511. The matching control circuit 511 comparesthe voltage inputted from the impedance detector 508 with the referencevoltage, and then supplies a voltage consistent with the differencetherebetween to the motor 512 for driving the matching variablecondenser 502. The matching variable condenser 502 is adjusted by themotor 512 so that the absolute value of impedance consequently equals apredetermined value, generally 50 Ω.

[0044] In the actual adjustment of impedance, however, when the tuningvariable condenser 503 and the matching variable condenser 502 of thefirst matching box 604 are changed, for example, the phase of impedanceand the absolute value of impedance detected in the second matching box616 are changed. Therefore, the tuning variable condenser 503 and thematching variable condenser 502 of the second matching box 616 arechanged, but on the other hand the phase of impedance and the absolutevalue of impedance detected in the first matching box 604 are alsochanged. With such a situation being repeated, the impedance of eachmatching box may be subjected to constant fluctuations. If thissituation is brought about, the produced plasma is not stabilized, andin some cases, plasma processing characteristics are adversely affectedsignificantly.

[0045] As another method of adjusting the impedance, the powerreflectivity, namely the value of reflected power/incident power, at theinlet of the matching box is used. In this adjustment method, forexample, the capacity of the tuning variable condenser is changed toincrease or decrease the same, and the capacity of the tuning variablecondenser is further changed in the same way if the power reflectivityconsequently drops, or the capacity of the tuning variable condenser ischanged in the opposite way if the power reflectivity consequentlyincreases. The matching variable condenser is also controlled in thesame manner as described above to adjust the capacity of each variablecondenser to the impedance condition under which the minimum powerreflection power ratio is achieved.

[0046] This adjustment method may cause the following problems. Forexample, assume that the capacity of the tuning variable condenser issmaller than the matching impedance in the first matching box 604. Inthis situation, if the capacity of the tuning variable condenser ischanged so that it decreases, the power reflectivity is essentiallyincreased in accordance therewith, and upon reception of a signalindicating that the power reflectivity is increased, the motor should berotated inversely to change the capacity of the condenser in a reverseway so that it increases. In the case where the capacity of the tuningvariable condenser or the matching variable condenser is changed in thesecond matching box 616 at the same time, however, the powerreflectivity in the first matching box 604 may be erroneously consideredto have dropped in association with this change. This is due to the factthat the power supply system for the first high frequency power iscoupled to the power supply system for the second high frequency powervia the plasma. That is, when observing the load from the power supplysystem for the first high frequency power, the load is such that theplasma is combined with the output impedance of the power supply systemof the second high frequency power. Therefore, when the capacities ofthe tuning variable condenser and the matching variable condenser in thesecond matching box 616 are changed, it appears as if the load impedancewas changed if observing from the power supply system of the first highfrequency power.

[0047] Therefore, in the first matching box 604, the capacity of thetuning variable condenser is changed so that it further decreases,resulting in the capacity being still further deviated with respect tothe matching impedance. Such a phenomenon similarly occurs in adjustmentof the capacity of the matching variable condenser, and may also occurin the tuning variable condenser and the matching variable condenser ofthe second matching box 616. Therefore, in the first matching box 604and the second matching box 616, no matching point cannot be found for along time, and in some cases, the impedances of the first matching box604 and the second matching box 616 may take on values so largelydeviated with respect to the matching impedance that the plasma can nolonger be maintained, resulting in discharge break.

[0048] The phenomenon described above can occur more easily when thehigh frequency powers for a plurality of power supply systems havedifferent frequencies, and particularly in the VHF frequency band.

[0049] In this way, there is a problem such that the variation in plasmaprocessing characteristics due to inappropriately conducted impedanceadjustment is one of important factors in achieving the improvement ofplasma processing characteristics and the reduction in costs for plasmaprocessing. That is, the improvement of impedance adjustment techniquehas been a challenge in achieving the improvement of plasma processingcharacteristics and the reduction in costs for plasma processing.

[0050] Although a variety of devices have been made hitherto forimpedance adjustment, in this way, an adjustment method capable ofappropriately dealing with a sudden change in load impedance caused byabnormal discharge or the like during plasma processing has not beenproposed.

SUMMARY OF THE INVENTION

[0051] The object of the present invention is to solve the aboveproblems. Specifically, an object of the invention is to provide aplasma processing method and a plasma processing apparatus for plasmaprocessing an object to be processed, which is placed in a reactorcontainer, by decomposing a raw material gas introduced into the reactorcontainer by introducing a high frequency power outputted from a highfrequency power supply into the reactor container via a matching deviceand an electrode, wherein the impedance adjustment by the matchingdevice is achieved properly and stably, thus making it possible toachieve the improvement of plasma processing characteristics, theimprovement of reproducibility of plasma processing characteristics andthe reduction in costs for plasma processing.

[0052] As a result of vigorously conducting studies for achieving theabove object, the inventors have found that in the adjustment ofimpedance by the matching device, changing the impedance of eachvariable circuit element in the matching circuit only within apredetermined range (hereinafter often referred to as “predeterminedimpedance variable range”), adjusting the impedance so that a presetmatching goal condition is satisfied, and changing the impedancevariable range as the plasma processing proceeds are effective inachieving the above object.

[0053] The present invention provides a plasma processing methodcomprising introducing a high frequency power outputted from a highfrequency power supply into a reactor container via a matching deviceand an electrode, decomposing a raw material gas introduced into thereactor container by means of the high frequency power and processing anobject to be processed which is placed in the reactor container, whereinthe adjustment of impedance by the matching device during plasmaprocessing is controlled within a predetermined impedance variablerange, and the impedance variable range is changed as the plasmaprocessing proceeds.

[0054] Another object of the present invention is to provide a plasmaprocessing method comprising introducing high frequency powers into areactor container via electrodes from a plurality of power supplysystems having high frequency power supplies and matching devicescapable of changing impedances, decomposing a raw material gasintroduced into the reactor container by means of the high frequencypowers, and plasma processing a substrate to be processed which isplaced in the reactor container, wherein the adjustment of impedance byat least one matching device of the matching devices of the plurality ofpower supply system during plasma processing is automatically controlledwithin a predetermined impedance variable range.

[0055] Another object of the present invention is to provide a plasmaprocessing apparatus comprising a reactor container for plasmaprocessing a substrate to be processed, raw material gas supplying meansfor supplying a raw material gas to the reactor container, and aplurality of power supply systems for supplying high frequency powers tothe reactor container, wherein the plurality of power supply systemshave matching circuits capable of changing impedances and controlsystems for controlling the impedances of the matching circuits, thecontrol system being capable of storing a variable range setting valuefor limiting an impedance variable range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056]FIG. 1 shows an outline of a configuration in a matching device(matching box) capable of being used in the plasma processing method ofthe present invention;

[0057]FIGS. 2A and 2B are schematic diagrams showing an example of anapparatus (plasma processing apparatus) for producing light-receivingmembers for electrophotography based on a VHF plasma CVD method usingthe VHF band;

[0058]FIG. 3 is a schematic diagram showing an example of the apparatus(plasma processing apparatus) for producing light-receiving members forelectrophotography based on the plasma CVD method using the RF band;

[0059]FIGS. 4A and 4B are schematic diagrams showing an example of theapparatus (plasma processing apparatus) for producing light-receivingmembers for electrophotography based on the VHF plasma CVD method usingthe VHF band;

[0060]FIG. 5 shows an outline of an example of the configuration in thematching device (matching box) used in a conventional plasma processingapparatus;

[0061]FIG. 6A is a longitudinal sectional view showing anotherconventional plasma processing apparatus;

[0062]FIG. 6B is a transverse sectional view taken along the 6B-6B lineof FIG. 6A, which shows the plasma processing apparatus;

[0063]FIG. 7A is a longitudinal sectional view showing a plasmaprocessing apparatus according to the present invention; and

[0064]FIG. 7B is a transverse sectional view taken along the 7B-7B lineof FIG. 7A, which shows the plasma processing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] According to the present invention, the adjustment of impedanceby a matching device is carried out properly and stably, thus making itpossible to achieve the improvement of plasma processingcharacteristics, the improvement of reproducibility of plasma processingcharacteristics and the reduction in costs for plasma processing.

[0066] The present invention will be described in detail below.

[0067] According to the present invention, since the adjustment ofimpedance by the matching device is carried out within a predeterminedimpedance variable range, the adjustment of impedance of the matchingcircuit is carried out only within the impedance variable range even ifthe load impedance is significantly changed due to abnormal discharge orthe like, and therefore there is no significant deviation from thenormal impedance, thus making it possible to prevent problems such thatthe abnormal discharge is promoted, and that it takes much time for theimpedance to return to a proper value after the abnormal dischargeoccurs. In addition, the present invention is characterized in that thisimpedance variable range is changed as the plasma processing proceeds.This is to deal with the situation in which conditions in the reactorcontainer, for example conditions of wall surfaces in the early stage ofplasma processing differ from those after the plasma processing somewhatproceeds, and consequently the load impedance is changed as the plasmaprocessing proceeds. When the adjustment of impedance is carried outwithin the same impedance variable range throughout plasma processing,the impedance variable range should be set to be wide for dealing withthe situation in which the load impedance is changed as the plasmaprocessing proceeds. As a result, the adjustment of impedance may not beachieved properly and stably. Therefore, the present invention ischaracterized in that the adjustment of impedance by the matching deviceis carried out within a predetermined impedance variable range, and theimpedance variable range is changed as the plasma processing proceeds,and this feature allows the stability of plasma to be further improved,thus making it possible to achieve the improvement of plasma processingcharacteristics, the improvement of reproducibility of plasma processingcharacteristics and the reduction in costs for plasma processing.

[0068] In the present invention described above, it is more effective tosubstantially continuously change the impedance variable range as theplasma processing proceeds. In the case where the impedance variablerange is changed discontinuously, the impedance of the matching circuitmay also be changed substantially discontinuously as the impedancevariable range is changed if the impedance of the matching circuitbefore being changed is close to the demarcation of the variable range,and as a result, discontinuous matching may occur, thus making itimpossible to draw the best effect from the present invention. Thissituation tends to rise in plasma processing in which a plurality ofprocesses with different conditions is carried out continuously.Therefore, it is more effective to substantially continuously change theimpedance variable range especially when the conditions are steeplychanged among a plurality of processes.

[0069] In the present invention, it is further more effective to presetconditions as criteria for determining that matching has been obtainedto stop the adjustment of impedance, namely matching goal conditions,and change as necessary the matching goal conditions as the plasmaprocessing proceeds. The matching goal conditions are generally set withthe absolute value of impedance at the inlet of the matching circuit,the phase of impedance, the power reflectivity and combinations thereof,and when the detected value is within the preset range, it is determinedthat matching has been obtained to stop the adjustment of impedance ofthe matching circuit. If the preset range is too narrow, however, thedetected value at the time of plasma processing cannot be adjusted so asto be within the preset range, and the impedance of the matching circuitis continuously adjusted, thus making it difficult to maintain stableplasma in some cases. On the other hand, if the preset range is toowide, there may be cases where the adjustment of impedance is stopped inspite of the fact that matching is not sufficiently achieved, resultingin the situation in which efficiency of power supply drops, and desiredplasma characteristics cannot be obtained. In addition, there may becases where variations of impedance among plasma processing lots areincreased, and thus reproducibility of plasma processing characteristicsis insufficiently achieved.

[0070] Therefore, setting the matching goal conditions to proper valuesis also important in producing plasma of desired characteristics withstability and good reproducibility. In actual plasma processing, propermatching goal conditions are also changed as the plasma processingproceeds since conditions in the reactor container change as the plasmaprocessing proceeds, as described above. Conventionally, even whenproper matching goal conditions are changed as the plasma processingproceeds as described above, matching goal conditions are not changed tothe proper conditions, and matching goal conditions are set to be widerso that all the proper matching goal conditions throughout plasmaprocessing are included, which sometimes presets obstacles to theimprovement of reproducibility of plasma processing properties. Thus,the matching goal conditions are changed as necessary as the plasmaprocessing proceeds, whereby such obstacles can be eliminated to achievefurther improvements of reproducibility of plasma processingcharacteristics.

[0071] It is more effective to substantially continuously change thematching goal conditions as the plasma processing proceeds as in thecase of changing the impedance variable range. In the case where thematching goal conditions are changed discontinuously, the matchingconditions may also be changed discontinuously as the matching goalconditions are changed if the matching conditions before being changedare close to the demarcation of the matching goal conditions, and as aresult, thus making it impossible to draw the best effect from thepresent invention. This situation tends to rise in plasma processing inwhich a plurality of processes with different conditions is carried outcontinuously. Therefore, it is more effective to substantiallycontinuously change the matching goal conditions especially when theconditions are steeply changed among a plurality of processes.

[0072] Also, in the present invention, automatic control of theadjustment of impedance may be performed before and after the startingof plasma processing or may be performed only after the starting ofplasma processing. In the case where the automatic control is performedbefore and after the starting of plasma processing, the impedancevariable range for the matching circuit is preferably changed before andafter the plasma is produced because the load impedance maysignificantly be changed before and after the plasma is produced. On theother hand, in the case where the automatic control is started after thestarting of plasma processing, the impedance may be adjusted manually toproduce the plasma, or the plasma may be produced by determining theimpedance of each element in the matching circuit suitable forproduction of plasma, presetting the impedance of each element in thematching circuit to the determined value before producing the plasma,and then gradually increasing the output of the high frequency powersupply. In this case, the most suitable impedance of each element in thematching circuit during production of plasma somewhat varies dependingon conditions in the reactor container among plasma processing lots, butsubstantially detrimental effects are prevented by immediately startingthe automatic control after the plasma is produced. Furthermore, theplasma production may be detected with a method that has been wellknown, such as detection using visual observation and a photoreceptor,detection using fluctuation of pressure in the reactor container, anddetection using a change in load impedance.

[0073] The present invention described above can produce remarkableeffects when the frequency of high frequency power used in plasmaprocessing is not lower than 50 MHz and not higher 250 MHz. This ispresumably because plasma tends to suffer unevenness in this frequencyband, and if the adjustment of impedance of the matching circuit isinappropriately carried out, the evenness of plasma is easily affectedadversely. Also, if an abnormal discharge occurs, the abnormal dischargeis easily promoted in this frequency band as long as the impedance ofthe matching circuit is inappropriate, and therefore the promotion ofsuch abnormal discharge can effectively be curbed to obtain remarkableeffects of the present invention by applying the present invention inplasma processing using a high frequency power having a frequency notlower than 50 MHz and not higher than 250 MHz, although its mechanism isnot elucidated at the present time.

[0074] The present invention described above can produce remarkableeffects particularly when the object to be processed moves or rotates atleast temporarily during plasma processing. In the case where the objectto be processed moves or rotates during plasma processing, the loadimpedance is often changed in association therewith. When a cylindricalsubstrate is rotated while it is subjected to plasma processing, forexample, the relative position of the substrate in the reactor containeris often slightly changed due to the eccentricity during rotation. Inthis way, an abnormal discharge tends to occur when the relativeposition of the substrate is changed, and the load impedance is changedin association with the change of position. In the present invention,even if such abnormal discharge occurs, the impedance of the matchingcircuit is limited to around a proper value, and therefore problems suchthat the impedance of the matching circuit is significantly deviatedfrom the proper value, and the abnormal discharge is promoted, areprevented, thus making it possible to maintain stable plasma.

[0075] Also, the present invention can produce significant effectsparticularly when plasma processing is conducted for forming anelectrophotographic photosensitive member. This is presumably because ofthe following two factors. First, when the electrophotographicphotosensitive member is formed, a deposition film with thickness ofseveral tens μm is generally formed, and thus much time is required forplasma processing. Therefore, a sudden change in load impedance oftenoccurs due to an abnormal discharge or the like during plasmaprocessing, and the present invention may produce remarkable effects tocurb a harmful influence on plasma processing in association with thischange. In addition, because it takes much time to conduct plasmaprocessing, the load impedance is significantly changed with time duringplasma processing, and the effect of the present invention to properlyadjust the impedance with respect to this change with time may beremarkable particularly when the electrophotographic photosensitivemember is formed. Second, in formation of the electrophotographicphotosensitive member, a plurality processes of plasma processing withdifferent conditions such as gas species, pressure and high frequencypowers are carried out continuously. Furthermore, the term“continuously” refers to not just a situation in which plasma processingconditions are continuously changed while keeping the state of producedplasma, but a situation in which the discharge is stopped on a temporarybasis at the time of changing processing conditions, and thereafter theprocessing conditions are changed to produce the plasma again. It hasbeen found that in the case where a plurality of processes of plasmaprocessing with different conditions are carried out continuously, theproper impedance variable range or the proper matching goal condition isdifferent for each condition, and thus the impedance may be properlyadjusted throughout a series of plasma processing, resulting insatisfactory plasma processing being performed by using the presentinvention to set a proper impedance variable range or proper matchinggoal condition for each condition.

[0076] The present invention is a plasma processing method for plasmaprocessing a substrate to be processed, which is placed in a reactorcontainer, by decomposing a raw material gas introduced into the reactorcontainer by introducing high frequency powers into the reactorcontainer via electrodes from a plurality of power supply systems havinghigh frequency power, supplies and matching devices. In the plasmaprocessing method according to the present invention, the adjustment ofimpedance by at least one matching device, of the matching devicesprovided in the plurality of power supply systems, is carried out withautomatic control within a predetermined impedance variable range.

[0077] Also, the plasma processing apparatus according to the presentinvention comprises a reactor container for plasma processing asubstrate to be processed, raw material gas supplying means forsupplying a raw material gas to this reactor container, and a pluralityof power supply systems for supplying high frequency powers to thereactor container. Also, in the plasma processing apparatus according tothe present invention, a plurality of power supply systems have matchingcircuits capable of changing impedances, and control systems forcontrolling impedances of the matching circuits. The control system canstore variable range setting values for limiting impedance variableranges.

[0078] According to the plasma processing method and the plasmaprocessing apparatus having configurations described above, theadjustment of impedance by the matching device is carried out for eachvariable circuit element of the matching circuit within a predeterminedimpedance variable range. According to this plasma processing method,the matching of impedance is carried out only within the predeterminedimpedance variable range, and therefore the impedance of the matchingcircuit is prevented from being significantly deviated from the propervalue even when a plurality of high frequency powers are introduced intothe reactor container at the same time.

[0079] According to this plasma processing method, the impedance of eachmatching circuit is prevented from being significantly deviated from theproper value, and therefore the variation of apparent load impedance inone matching circuit due to the change of impedance of the othermatching circuit are limited to within some level of variation, thusmaking it possible to achieve stabilization of plasma. Also, theimpedance of the matching circuit is not fixed at a predetermined value,thus making it possible to keep track of a change in the load impedanceassociated with a change in conditions in the reactor containeroccurring as plasma processing proceeds.

[0080] Also, in the present invention, effects of stabilizing plasma canbe obtained by carrying out this adjustment of impedance in at least oneof a plurality of high frequency power supply systems, but thisadjustment of impedance is preferably carried out in all high frequencypower supply systems for obtaining remarkable effects.

[0081] Also, the present invention is particularly effective when aplurality of high frequency powers of different frequencies are suppliedto the reactor container at the same time, and is thus preferable. Thatis, in the case where a plurality of high frequency powers of differentfrequencies are supplied to the reactor container at the same time,interference between the power supply systems easily arises as describedabove, and stabilization of plasma becomes further difficult in theconventional method of adjusting the impedance, while the presentinvention can produce adequate effects of stabilizing the plasma even inthis case.

[0082] Also, the plasma processing method according to the presentinvention can produce further more remarkable effects when a pluralityof high frequency powers are supplied to the reactor container from thesame high frequency electrode at the same time, and is thus preferable.In the case where a plurality of high frequency powers are supplied tothe reactor container from the same high frequency electrode at the sametime, the power supply systems are electrically coupled to one anotherdirectly through the high frequency electrode and therefore interferencemore easily arises, and stabilization of plasma becomes furtherdifficult in the conventional method of adjusting the impedance, whilethe present invention can produce adequate effects of stabilizing theplasma even in this case.

[0083] Also, in the plasma processing method according to the presentinvention, preferably two types of high frequency powers havingfrequencies not lower than 10 MHz and not higher than 250 MHz aresupplied, respectively, when a plurality of different high frequencypowers are supplied to the reactor container at the same time, andprovided that the frequency of the high frequency power having a higherfrequency is represented by f₁ and the frequency of the high frequencypower having a lower frequency is represented by f₂, preferably thecondition of 0.1≦f₂/f₁≦0.9, more preferably the condition of0.5<f₂/f₁≦0.9 is satisfied. In these conditions, the interferencedescribed above easily arises in general, and thus the dischargeinstability is significantly increased, but by applying the presentinvention, the influence of this interference can remarkably beinhibited, and as a result, a stable discharge can be maintained.

[0084] For specific embodiments of the present invention, the plasmaprocessing apparatus and the method of forming a deposition film will bedescribed below with reference to the drawings.

[0085]FIG. 1 shows an outline of a configuration in a matching device(matching box) capable of being used in the present invention. Thematching device is constituted by a system including a matching circuit101 and a control system 100. The matching circuit 101 is constituted bya matching variable condenser 102, a tuning variable condenser 103 and acoil 104, and at the inlet of the matching circuit 101, a high frequencycurrent is detected by a current detection element 105 and a highfrequency voltage is detected by a voltage detection element 106. Theoutputs of the current detection element 105 and the voltage detectionelement 106 are inputted to a phase difference detector 107 and animpedance detector 108 in the control system 100. In the phasedifference detector 107, the phase of impedance at the inlet of thematching circuit 101 is detected, and a voltage consistent with thephase of impedance is outputted to an impedance/phase control unit 109.In the impedance/phase control unit 109, the impedance of the tuningvariable condenser 103 is controlled within a predetermined variablerange based on the voltage inputted from the phase difference detector107. Specifically, the voltage inputted from the phase differencedetector 107 is compared with a reference voltage, and a voltageconsistent with the difference therebetween is supplied to a motor 110for driving the tuning variable condenser 103. In this case, when theimpedance of the tuning variable condenser 103 reaches the maximum orminimum value in the predetermined variable range, the impedance/phasecontrol unit 109 immediately stops supplying the voltage to the motor110. Also, if the impedance of the tuning variable condenser 103 hasalready reached the maximum value in the predetermined variable range,the impedance/phase control unit 109 conducts the supply of voltage tothe motor 110 for decreasing the impedance of the tuning variablecondenser 103, but does not conduct the supply of voltage for increasingthe impedance of the tuning variable condenser 103. Similarly, if theimpedance of the tuning variable condenser 103 has already reached theminimum value in the predetermined variable range, the impedance/phasecontrol unit 109 conducts the supply of voltage to the motor 110 forincreasing the impedance of the tuning variable condenser 103, but doesnot conduct the supply of voltage for decreasing the impedance of thetuning variable condenser 103. In this way, the impedance of the tuningvariable condenser 103 is controlled within a predetermined variablerange so that the phase of impedance at the inlet of the matchingcircuit 101 may be within the predetermined range, and if matching goalconditions are not satisfied within the predetermined range, theadjustment of impedance of the tuning variable condenser 103 is stoppedwith the phase being closest to the matching goal condition.

[0086] On the other hand, in the impedance detector 108, the absolutevalue of impedance at the inlet of the matching circuit 101 is detected,and a voltage consistent with the absolute value of impedance isoutputted to the impedance/phase control unit 109. In theimpedance/phase control unit 109, the voltage inputted from theimpedance detector 108 is compared with a reference voltage, and avoltage consistent with the difference therebetween is supplied to amotor 112 for driving the matching variable condenser 102. In this case,the impedance/phase control-unit 109 stops supplying the voltage to themotor 112 at the time when the impedance of the matching variablecondenser 102 reaches the maximum or minimum value in the predeterminedvariable range. Also, if the impedance of the matching variablecondenser 102 has already reached the maximum value in the predeterminedvariable range, the impedance/phase control unit 109 conducts the supplyof voltage to the motor 112 for decreasing the impedance of the matchingvariable condenser 102, but does not conduct the supply of voltage forincreasing the impedance of the matching variable condenser 102.Similarly, if the impedance of the matching variable condenser 102 hasalready reached the minimum value in the predetermined variable range,the impedance/phase control unit 109 conducts the supply of voltage tothe motor 112 for increasing the impedance of the matching variablecondenser 102, but does not conduct the supply of voltage for decreasingthe impedance of the matching variable condenser 102. In this way, theimpedance of the matching variable condenser 102 is controlled within apredetermined variable range so that the absolute value of impedance atthe inlet of the matching circuit 101 may be within the predeterminedrange, and if matching goal conditions are not satisfied within thepredetermined range, the adjustment of impedance of the matchingvariable condenser 102 is stopped with the impedance being closest tothe matching goal condition.

[0087] By this control, the adjustment of impedance is carried out withautomatic control in a predetermined impedance variable range.Furthermore, for the method of detecting the impedances of the tuningvariable condenser 103 and the matching variable condenser 102, a methodthat has been well known may be used, such as a method in which theshift amounts of a variable condenser and a mechanical unit for drivingthe condenser are detected, and a method in which a stepping motor isused as a motor for driving the variable condenser to detect theimpedance based on its drive signal. Also, the impedances of the tuningvariable condenser 103 and the matching variable condenser 102 do notnecessarily need to be always detected, but instead the signal may beoutputted to the impedance/phase control unit 109 at the time when theimpedances of the tuning variable condenser 103 and the matchingvariable condenser 102 reach maximum or minimum value in the variablerange.

[0088] Furthermore, the term “impedance variable range” in the presentinvention does not refer to an impedance variable range limited in termsof configuration by the variable width of impedance variable elementsconstituting the matching circuit, but an impedance variable rangedetermined independently thereof.

[0089] By determining an impedance variable range independently of thevariable width of impedance variable elements in this way, the impedancevariable range can be set to a desired range with high accuracy, and theset range can be changed easily. As a result, discharge stability duringvacuum processing can be improved, and the determined impedance variablerange can be changed during vacuum processing, thus making it possibleto accommodate even a plurality processes being carried outcontinuously.

[0090] The plasma processing using a matching box having a configurationshown in FIG. 1 can be conducted according to the following procedurewhen an electrophotographic photosensitive member constituted by acharge injection blocking layer, a photoconductive layer and a surfacelayer is formed, using a plasma processing apparatus as shown in FIGS.4A and 4B.

[0091] First, prior to formation of the electrophotographicphotosensitive member, the impedance of the matching variable condenser102 and the impedance of the tuning variable condenser 103 at whichplasma is maintained with stability are determined through a preliminaryexperiment in advance including variations among lots, for conditions ofeach of the charge injection blocking layer, photoconductive layer andsurface layer, and the impedance variable range of the matching variablecondenser 102 and the impedance variable range of the matching variablecondenser 103 of each layer are determined based on the result of thepreliminary experiment. The impedance variable range is determined asappropriate in accordance with plasma formation conditions, theconfiguration of apparatus to be used, and the like, in such a mannerthat just the range of variations, or fluctuations of the impedance ofthe matching variable condenser 102 and the impedance of the tuningvariable condenser 103 obtained from the preliminary experiment isdefined as the variable range, or a range approximately twice as wide asthe range of variations of impedance is defined as the impedancevariable range, for example, so that plasma can be maintained withstability in actual plasma processing.

[0092] According to considerations by the inventors, it is preferablethat the impedance variable range is set within a range approximatelytwice as wide as the range of variations of impedance obtained from thepreliminary experiment in maintaining stable plasma. If the impedance ofthe variable condenser varies between 200 pF and 300 pF according to thepreliminary experiment, namely the width of variations of impedance is100 pF, for example, the impedance variable range of the variablecondenser is preferably set to a range twice as wide as the range ofvariations, namely the width of 200 pF, and in the case of this example,the impedance variable range of the variable condenser is preferably setwithin the range of from 150 pF to 350 pF.

[0093] The impedance variable range of the matching variable condenser102 and the impedance variable range of the tuning variable condenser103 of each of the charge injection blocking layer, photoconductivelayer and surface layer determined in this way are stored in theimpedance/phase control unit 109 in advance, and the impedance variablerange of the matching variable condenser 102 and the impedance variablerange of the matching condenser 103 may be changed in accordance withthe timing of switching of layers, or data may be sent from the outsideto the impedance/phase control unit 109 in accordance with the timing ofswitching of layers, or the impedance variable range may be changed byother methods.

[0094] Also, the number of impedance variable ranges for each layer isnot necessarily one, but instead two or more impedance variable layersmay be set for each layer. In this case, the impedance variable range isswitched to the next impedance variable range at a predeterminedmidpoint of the layer. Conversely, different impedance variable rangesare not necessarily set for different layers, but instead, for example,the same impedance variable range may be used for the charge injectionblocking layer and the photoconductive layer, or the same impedancevariable range may be used for the photoconductive layer and the surfacelayer, or the same impedance variable range may be used for the blockinglayer and the initial portion of the photoconductive layer and theimpedance variable range may be changed at some midpoint of thephotoconductive layer, although the impedance variable range should bechanged at least at one point in a series of plasma processing.

[0095] Timing for changing the impedance variable range may bedetermined as appropriate, but it is preferable that the impedancevariable range is changed at the time when a remarkable change in loadimpedance occurs as plasma processing proceeds in obtaining remarkableeffects of the present invention.

[0096] After the impedance variable range is determined in advance inthis way, cylindrical substrates 405 are placed in a reactor container401, and gas in the reactor container 401 is exhausted through anexhaust pipe 411 by an exhausting system (not shown) in a plasmaprocessing apparatus shown in FIGS. 4A and 4B. Subsequently, thecylindrical substrate 405 is rotated with a motor 409 via a rotationshaft 408, and the cylindrical substrate 405 is heated by a heatingelement 407 while control is performed so that it is kept at apredetermined temperature of about 200 to 300° C.

[0097] When the temperature of the cylindrical substrate 405 reaches apredetermined temperature, a raw material gas for use in formation ofthe charge injection blocking layer is introduced into the reactorcontainer 401 via raw material gas supplying means 412. After it ischecked that the flow rate of the raw material gas reaches a preset flowrate, and the pressure in the reactor container 401 is stabilized, theoutput of the high frequency power supply 403 is set at a predeterminedvalue. Subsequently, the impedances of the matching variable condenser102 and the tuning variable condenser 103 are adjusted so that theoutput voltage from the phase detector 107 shown in FIG. 1 and theoutput voltage from the impedance detector 108 approach to referencevalues, or the power reflectivity observed by watching a power meter isreduced. In addition, the variable range does not necessarily need to beset for the impedances of the matching variable condenser 102 and thetuning variable condenser 103, but it is more preferable that theimpedance variable range is set for the impedances in reducing theamount of adjustment time and curbing the variations among lots ofplasma processing characteristics. In addition, it is preferable thatthe impedances of the matching variable condenser 102 and the tuningvariable condenser 103 at the time when the adjustment of impedance isstarted are set at values at which the discharge is most easilyproduced, and the adjustment of impedance is carried out with the valuesas starting points in reducing the amount of adjustment time and curbingthe variations among lots of plasma processing characteristics.

[0098] Through this adjustment of impedance, the high frequency power isefficiently supplied to the reactor container 401 via a cathode (highfrequency electrode) 402, and plasma is produced in a film formationspace 406 surrounded by the cylindrical substrates 405. When the plasmais produced, the impedance variable ranges for the matching variablecondenser 102 and the tuning variable condenser 103 are set at values atthe time when formation of the charge injection blocking layer isstarted, and the adjustment of impedance is carried out. At this time,the impedance variable ranges for the matching variable condenser 102and the tuning variable condenser 103 are preferably impedance variableranges in which the values of impedances of the matching variablecondenser 102 and the tuning variable condenser 103 at the time when theplasma is produced are included.

[0099] Also, the proper impedances of the matching variable condenser102 and the tuning variable condenser 103 may significantly be variedbefore and after the plasma is produced. In this case, the variableranges for impedances of the matching variable condenser 102 and thetuning variable condenser 103 at the time when formation of the chargeinjection blocking layer is started must be set to be wide, andtherefore during formation of the charge injection blocking layer, thevariable ranges are preferably changed continuously or in stages so thatthe impedance variable ranges are gradually narrowed.

[0100] When the formation of the charge injection blocking layer iscompleted, then the photoconductive layer is formed. In the case wherethe discharge is stopped between the charge injection blocking layer andthe photoconductive layer, the supply of high frequency power is stoppedafter a charge injection blocking layer having a desired thickness isformed, and then the supply of raw material gas is stopped to completethe formation of the charge injection blocking layer. Then, thephotoconductive layer is formed using the same procedure as that usedwhen the formation of the charge injection blocking layer was started.At this time, the plasma processing condition, the impedance variablerange and the matching goal condition as required are changed to thosefor formation of the photoconductive layer.

[0101] On the other hand, in the case where the charge injectionblocking layer and the photoconductive layer are continuously formedwithout cutting off the discharge, plasma processing conditions such asthe flow rate of raw material gas, the high frequency power and pressureare changed continuously and/or in stages to set conditions forformation of the photoconductive layer. How to change the plasmaprocessing condition is not particularly limited, and may be determinedas appropriate observing the plasma processing characteristics. Also,for changing the impedance variable range at the time of transition fromthe charge injection blocking layer to the photoconductive layer, forexample, the impedance variable range during formation of the chargeinjection blocking layer, the impedance variable range when theprocessing condition is changed, and the impedance variable range duringformation of the photoconductive layer may be set at different values,or the impedance variable range during formation of the charge injectionblocking layer may be employed until the changing of the processingcondition is completed, and the impedance variable range for formationof the photoconductive layer may be set at the time when formation ofthe photoconductive layer is started, or the impedance variable rangefor formation of the photoconductive layer may be set at the time whenthe formation of the charge injection blocking layer is completed, andthe same impedance variable range may be employed during the changing ofthe processing condition and during formation of the photoconductivelayer. In the case where the impedance variable range during formationof the charge injection blocking layer, the impedance variable rangeduring the changing of the processing condition, and the impedancevariable range during formation of the photoconductive layer are set atdifferent values, for example, a plurality of impedance variable rangesmay be set for those during the changing of the processing condition,and the impedance variable range may be changed also during the changingof the processing condition. Because the suitable process for changingthe impedance variable range varies depending on desired processingcharacteristics, plasma processing conditions, configurations of plasmaprocessing apparatus and the like, how to change the impedance variablerange may be determined as appropriate in consideration with thesefactors, but in any case, the impedance variable range should be changedat least at one point in a series of plasma processing.

[0102] When the formation of the photoconductive layer is completed inthis way, the surface layer is subsequently formed. The procedure oftransition from the formation of the photoconductive layer to theformation of the surface layer may be the same as the procedure oftransition from the formation of the charge injection blocking layer tothe formation of the photoconductive layer.

[0103] When the formation of the surface layer is completed in this way,the output of high frequency power is stopped, and the supply of rawmaterial gas is stopped to complete the formation of theelectrophotographic photosensitive member.

[0104] Furthermore, for the changing of the impedance variable range,both the impedance variable ranges for the matching variable condenser102 and the tuning variable condenser 103 may be changed or any onethereof may be changed.

[0105] Plasma processing using the matching box having the configurationshown in FIG. 1 may be performed in the following way in the case where,for example, the plasma processing apparatus shown in FIGS. 6A and 6B isused to form an electrophotographic photosensitive member constituted ofthe charge injection blocking layer, photoconductive layer and surfacelayer. Furthermore, matching boxes 604 and 616 in FIG. 6A both have theinternal configuration shown in FIG. 1, but in order to discriminatebetween members in the matching box 604 and members in the matching box616, the members in the matching box 604 will be given a symbol “a” andthe members in the matching box 616 will be given a symbol “b” forconvenience in the description below.

[0106] First, prior to formation of the electrophotographicphotosensitive member, the impedance of a matching variable condenser102 a and the impedance of a tuning variable condenser 103 a in thematching box 604 at which plasma is maintained with stability aredetermined through a preliminary experiment in advance includingvariations among lots for conditions of each of the charge injectionblocking layer, photoconductive layer and surface layer, and theimpedance variable range of the matching variable condenser 102 a andthe impedance variable range of the matching variable condenser 103 a ofeach layer are determined based on the result of the preliminaryexperiment. The impedance variable range is determined as appropriate inaccordance with plasma formation conditions, the configuration ofapparatus to be used, in such a manner that just the range of variationsor fluctuations of the impedance of the matching variable condenser 102a and the impedance of the tuning variable condenser 103 a obtained fromthe preliminary experiment is defined as the variable range, or a rangeapproximately twice as wide as the range of variations of impedance isdefined as the impedance variable range, for example, so that plasma canbe maintained with stability in actual plasma processing. According tothe present invention, it is preferable that the impedance variablerange is set within a range approximately twice as wide as the range ofvariations of impedance obtained from the preliminary experiment inmaintaining stable plasma. If the impedance of the variable condenservaries between 200 pF and 300 pF according to the preliminaryexperiment, namely the width of variations of impedance is 100 pF, forexample, the impedance variable range of the variable condenser ispreferably set to a range twice as wide as the range of variations orfluctuations, namely the width of 200 pF, and in the case of thisexample, the impedance variable range of the variable condenser is setwithin the range of from 150 pF to 350 pF.

[0107] Similarly, the impedance of a matching variable condenser 102 band the impedance of a tuning variable condenser 103 b in the matchingbox 616 are determined through a preliminary experiment in advanceincluding variations among lots, and the impedance variable range of thematching variable condenser 102 b and the impedance variable range ofthe matching variable condenser 103 b of each layer are determined basedon the result of the preliminary experiment. The specific impedancevariable range is determined in the same manner as the matching box 604.

[0108] The impedance variable ranges of the matching variable condensers102 a and 102 b and the impedance variable ranges of the tuning variablecondensers 103 a and 103 b of each of the charge injection blockinglayer, photoconductive layer and surface layer determined in this wayare stored in impedance/phase control units 109 a and 109 b in advance,and the impedance variable ranges of the matching variable condensers102 a and 102 b and the impedance variable ranges of the matchingcondensers 103 a and 103 b may be changed in accordance with the timingof switching of layers, or data may be sent from the outside to theimpedance/phase control units 109 a and 109 b in accordance with thetiming of switching of layers, or the impedance variable ranges may bechanged by other methods.

[0109] Also, the number of impedance variable ranges for each layer isnot necessarily one, but instead two or more impedance variable layersmay be set for each layer. In this case, the impedance variable range isswitched to the next impedance variable range at a predeterminedmidpoint of the layer. Conversely, different impedance variable rangesare not necessarily set for different layers, but instead, for example,the same impedance variable range may be used for the charge injectionblocking layer and the photoconductive layer, or the same impedancevariable range may be used for the photoconductive layer and the surfacelayer, or the same impedance variable range may be used for the blockinglayer and the initial portion of the photoconductive layer and theimpedance variable range may be changed at some midpoint of thephotoconductive layer, or the same impedance variable range may be usedfor all the layers. Furthermore, for obtaining remarkable effects of thepresent invention, it is preferable that at a suitable point inprocessing, the impedance variable range is changed to the optimalimpedance variable range at this point.

[0110] Timing for changing the impedance variable range may bedetermined as appropriate, but it is preferable that the impedancevariable range is changed at the time when a remarkable change in loadimpedance occurs as plasma processing proceeds in obtaining remarkableeffects of the present invention.

[0111] The changing of the impedance variable range is not necessarilysynchronized for the matching box 604 and the matching box 616, buttiming may be different for each of the matching boxes.

[0112] After the impedance variable range is determined in advance inthis way, cylindrical substrates 605 are placed in a reactor container601, and gas in the reactor container 601 is exhausted through anexhaust pipe 611 by an exhausting system (not shown). Subsequently, thecylindrical substrate 605 is rotated with a motor (not shown) via arotation shaft 608, and the cylindrical substrate 605 is heated by aheating element 607 while control is performed so that it is kept at apredetermined temperature of about 200 to 300° C.

[0113] When the cylindrical substrate 605 is heated to a predeterminedtemperature, a raw material gas for use in formation of the chargeinjection blocking layer is introduced into the reactor container 601via a raw material gas supply pipe 612. After it is checked that theflow rate of the raw material gas reaches a preset flow rate, and thepressure in the reactor container 601 is stabilized, the outputs of thehigh frequency power supplies 603 and 615 are set at predeterminedvalues.

[0114] When high frequency powers are outputted from the high frequencypower supplies 603 and 615, the adjustment of impedance is carried outin the matching boxes 604 and 616. Specifically, the impedances of thematching variable condensers 102 a and 102 b and the tuning variablecondensers 103 a and 103 b are adjusted, respectively, so that theoutput voltages from phase detectors 107 a and 107 b, and the outputvoltages from impedance detectors 108 a and 108 b are close to referencevoltages. Through this adjustment of impedance, high frequency powersare efficiently supplied to the reactor container 601 via high frequencyelectrodes 602 and 614, and plasma is produced in the reactor container601.

[0115] Furthermore, this adjustment of impedance during production ofplasma is not necessarily carried out automatically. For example, theadjustment of impedance may be carried out manually during production ofplasma, and then the operation may be switched to automatic controlafter it is checked that the plasma has been produced, or plasma may beproduced by manually adjusting the impedance, and then the operation maybe switched to automatic control after predetermined time elapses.

[0116] In addition, when plasma is produced by automatically adjustingthe impedance, the variable range is not necessarily set for theimpedances of the matching variable condensers 102 a and 102 b, and thetuning variable condensers 103 a and 103 b from the time when theproduction of plasma is started. For example, the impedance variablerange may not be set when plasma is produced, and the impedance variablerange may be set only after predetermined time elapses after the plasmais produced.

[0117] In addition, it is preferable that the impedances of the matchingvariable condensers 102 a and 102 b and the tuning variable condenser103 a and 103 b at the time of producing plasma are set at values atwhich the discharge is most easily produced, and the adjustment ofimpedance is carried out with the values as starting points in reducingthe amount of adjustment time and curbing the variations among lots ofplasma processing characteristics.

[0118] When the plasma is produced in this way, the impedance variableranges for the matching variable condensers 102 a and 102 b and thetuning variable condensers 103 a and 103 b are set at values at the timewhen formation of the charge injection blocking layer is started, andthe adjustment of impedance is carried out. At this time, the impedancevariable ranges for the matching variable condensers 102 a and 102 b andthe tuning variable condensers 103 a and 103 b are preferably impedancevariable ranges in which the values of impedances of the matchingvariable condensers 102 a and 102 b and the tuning variable condensers103 a and 103 b are included.

[0119] Also, the proper impedances of the matching variable condensers102 a and 102 b and the tuning variable condensers 103 a and 103 b maysignificantly be varied before and after the plasma is produced. In thiscase, the variable ranges for impedances of the matching variablecondensers 102 a and 102 b and the tuning variable condensers 103 a and103 b at the time when formation of the charge injection blocking layeris started must be set to be wide, and therefore during formation of thecharge injection blocking layer, the variable ranges are preferablychanged continuously or in stages so that the impedance variable rangesare gradually narrowed.

[0120] After the formation of the charge injection blocking layer iscompleted, then the photoconductive layer is formed. In the case wherethe discharge is stopped between the charge injection blocking layer andthe photoconductive layer, the supply of high frequency power is stoppedafter a charge injection blocking layer having a desired thickness isformed, and then the supply of raw material gas is stopped to completethe formation of the charge injection blocking layer. Then, thephotoconductive layer is formed through the same step as that taken whenthe formation of the charge injection blocking layer was started. Atthis time, the plasma processing condition, the impedance variablerange, and the matching goal condition as required are changed to thosefor formation of the photoconductive layer.

[0121] On the other hand, in the case where the charge injectionblocking layer and the photoconductive layer are continuously formedwithout cutting off the discharge, plasma processing conditions such asthe flow rate of raw material gas, the high frequency power and pressureare changed continuously and/or in stages to set conditions forformation of the photoconductive layer. How to change the plasmaprocessing condition is not particularly limited, and may be determinedas appropriate observing the plasma processing characteristics. Also,for changing the impedance variable range at the time of transition fromthe charge injection blocking layer to the photoconductive layer, forexample, the impedance variable range during formation of the chargeinjection blocking layer, the impedance variable range when theprocessing condition is changed, and the impedance variable range duringformation of the photoconductive layer may be set at different values,or the impedance variable range during formation of the charge injectionblocking layer may be employed until the changing of the processingcondition is completed, and the impedance variable range for formationof the photoconductive layer may be set at the time when formation ofthe photoconductive layer is started, or the impedance variable rangefor formation of the photoconductive layer may be set at the time whenthe formation of the charge injection blocking layer is completed, andthe same impedance variable range may be employed during the changing ofthe processing condition and during formation of the photoconductivelayer. In the case where the impedance variable range during formationof the charge injection blocking layer, the impedance variable rangeduring the changing of the processing condition, and the impedancevariable range during formation of the photoconductive layer are set atdifferent values, for example, a plurality of impedance variable rangesmay be set for those during the changing of the processing condition,and the impedance variable range may be changed during the changing ofthe processing condition. Because the suitable process for changing theimpedance variable range varies depending on desired plasma processingcharacteristics, plasma processing conditions, configurations of plasmaprocessing apparatus and the like, how to change the impedance variablerange may be determined as appropriate in consideration with thesefactors.

[0122] When the formation of the photoconductive layer is completed inthis way, the surface layer is subsequently formed. The procedure oftransition from the formation of the photoconductive layer to theformation of the surface layer may be the same as the procedure oftransition from the formation of the charge injection blocking layer tothe formation of the photoconductive layer.

[0123] When the formation of the surface layer is completed in this way,the output of high frequency power is stopped, and the supply of rawmaterial gas is stopped to complete the formation of theelectrophotographic photosensitive member.

[0124] Furthermore, for the changing of the impedance variable range,both the impedance variable ranges for the matching variable condensers102 a and 102 b and the tuning variable condensers 103 a and 103 b maybe changed or any one thereof may be changed.

[0125] Also, in the plasma processing method, two types of highfrequency powers having frequencies not lower than 10 MHz and not higherthan 250 MHz are supplied, respectively, when a plurality of differenthigh frequency powers are supplied to the reactor container at the sametime, and provided that the frequency of the high frequency power havinga higher frequency is represented by f₁ and the frequency of the highfrequency power having a lower frequency is represented by f₂, thecondition of 0.1≦f₂/f₁≦0.9 is preferably satisfied. The reason for thiswill be described below.

[0126] In the case where a power having a VHF band or a frequency aroundthe VHF band is used to produce plasma to carry out vacuum processing,the wavelength of high frequency power in a vacuum processing containerhas a length approximately as large as the vacuum processing ontainer, ahigh frequency electrode, a substrate, a substrate holder or the like,and the high frequency power is apt to form a standing wave in thevacuum processing container, and this standing wave causes the strengthof power and thus plasma characteristics to vary area by area in thevacuum processing container. Consequently, it is difficult to keepvacuum processing characteristics uniform over a wide range of area.

[0127] As a measure to solve this problem, there is a method in which aplurality of high frequency powers of different frequencies is suppliedto the reactor container at the same time. In this way, a plurality ofstanding waves of different wavelengths consistent with the respectivefrequencies are formed in the reactor container, but they are suppliedat the same time, and therefore these standing waves are combined, sothat a distinct standing wave is no longer formed.

[0128] However, if the frequencies of a plurality of high frequencypowers are different in one order of magnitude or greater, the processin which the raw material gas is decomposed with high frequency powersof higher frequencies differs from the process in which the raw materialgas is decomposed with high frequency powers of lower frequencies, andas a result, the types and ratios of generated active species aredifferent. Therefore, even though uniformity is achieved in terms ofelectric field strength, active species of types and ratios consistentwith higher frequencies are generated in large quantities in the loopregions of standing waves formed with high frequency powers of higherfrequencies, and active species of types and ratios consistent withlower frequencies are generated in large quantities in the loop regionsof standing waves formed with high frequency powers of lowerfrequencies. As a result, spatial distributions may arise in the typeand ratio of active species, resulting in unevenness in vacuumprocessing characteristics.

[0129] On the other hand, the relationship between frequencies f₁ and f₂is limited to f₂/f₁≧0.1, whereby the level of difference in types andratios of generated active species caused by the difference infrequencies is reduced to a level that does not cause a problem from aviewpoint of practical use, thus making it possible to achieve a highlevel of evenness in vacuum processing characteristics.

[0130] Also, if the frequencies f₁ and f₂ are too close to each other,the node position and loop position of each standing wave are close toeach other, and therefore adequate effects of inhibiting electric fieldstanding waves can no longer be obtained. Therefore, it is alsonecessary to limit the relationship between frequencies f₁ and f₂ to0.9≧f₂/f1 in obtaining a high level of evenness in vacuum processingcharacteristics.

[0131] In addition, if the frequency f₁ is higher than 250 MHz, theremay be cases where attenuation of power in the onward direction issignificant, and thus there arise considerable differences inattenuation factors between high frequency powers having differentfrequencies, thus making it impossible to obtain adequate effects ofachieving evenness. In addition, if the frequency f₂ is lower than 10MHz, the vacuum processing speed rapidly decreases, resulting in apreferred situation in terms of cost.

[0132] From the above, it is very effective in maintaining the vacuumprocessing speed at a high level while improving evenness in vacuumprocessing characteristics to limit the relationship between thefrequencies f₁ and f₂ to the following inequality.

250 MHz>f1>f2≧10 MHz

0.9≧f2/f1≧0.1

[0133] However, if a plurality of high frequency powers in the abovefrequency range is used, interference tends to occur as describedpreviously, and plasma stability may be insufficient in the conventionalmethod of adjusting the impedance.

[0134] In contrast to this, in the method of the present invention ofadjusting the impedance, the influence by this interference is curbed toenable the plasma to be maintained with stability and goodreproducibility, and therefore a problem found when the conventionalmethod of adjusting the impedance is solved, thus making it possible toobtain generally excellent vacuum processing characteristics with highevenness and less variations in vacuum processing characteristics.

[0135] In addition, the frequencies of high frequency powersparticularly preferably satisfy the condition of 0.5<f₂/f₁≦0.9. Bysetting this range, the effect of improving evenness is furtherenhanced, and plasma stability is ensured by the method of the presentinvention of adjusting the impedance, thus making it possible togenerally excellent vacuum processing characteristics.

[0136] According to the above described plasma processing apparatus andplasma processing method, the adjustment of impedance by the matchingdevice is carried out automatically in a predetermined impedancevariable range, and thereby the matching of impedance by the matchingdevice is carried out properly and stably, thus making it possible toachieve the improvement of plasma processing characteristics, theimprovement of reproducibility of plasma processing characteristics andreduction in cost for plasma processing.

[0137] The plasma processing apparatus according to the presentinvention is a plasma processing apparatus capable of supplying aplurality of high frequency powers to the reactor container at the sametime, and is identical in basic configuration to the plasma processingapparatus shown in FIGS. 6A and 6B.

[0138] Furthermore, the plasma processing apparatus according to thepresent invention may be applied for another plasma processing apparatuscomprising a dielectric wall. Another plasma processing apparatusaccording to the present invention will be described with reference tothe drawings.

[0139]FIG. 7A is a cross sectional view of the plasma processingapparatus, and FIG. 7B is a cross sectional view taken along the 7B-7Bline in FIG. 7A. An exhaust port 709 is provided in the bottom of areactor container 701, and the other end of this exhaust port 709 isconnected to an exhaust system (not shown).

[0140] Twelve cylindrical substrates 705 on which a deposition film isto be formed are installed while being placed on a holder 706, in such amanner as to surround the central portion and in parallel with oneanother in the reactor container 701 provided in this plasma processingapparatus.

[0141] Each cylindrical substrate 705 is supported by a rotation shaft708, and is heated by a heating element 707. By driving a motor (notshown), the rotation shaft 708 is rotated, and the cylindrical substrate705 is thereby rotated around the central axis in the bus line directionthereof. The cylindrical substrate 705 is kept at a ground potentialthrough the rotation shaft 708. A raw material gas is supplied from araw material gas supply pipe 710 to the reactor container 701.

[0142] A cylindrical dielectric wall 703 made of alumina is provided ina part of reactor container 701. Six rod-shaped high frequencyelectrodes 702 are installed in parallel with one another outside thecylindrical dielectric wall 703, and a high frequency power shield 704is provided outside these high frequency electrodes 702.

[0143] The high frequency power outputted from a high frequency powersupply 711 is supplied to the high frequency electrode 702 via amatching box 712. The high frequency power supply 711 and the matchingbox 712 are electrically connected together via a coaxial cable. Also,the high frequency power outputted from a high frequency power supply713 Is supplied to the high frequency electrode 702 via a matching box714. The high frequency power supply 713 and the matching box 714 areelectrically connected together via a coaxial cable.

[0144] Also, the matching boxes provided in this plasma processingapparatus each have a configuration identical to that of the matchingbox shown in FIG. 1, and there description thereof is not presentedhere.

EXAMPLES

[0145] The present invention will be more in detail below usingExamples, but the present invention is not limited thereto.

Example 1

[0146] Using a plasma processing apparatus shown in FIGS. 4A and 4B anda matching box of a matching device having a configuration shown in FIG.1, ten lots of a-Si based photosensitive members (total 60 members) eachconstituted of a charge injection blocking layer, a photoconductivelayer and a surface layer were fabricated on cylindrical substrates 405each being an aluminum cylinder having a diameter of 80 mm and a lengthof 358 mm in accordance with the conditions shown in Table 1, with theoscillation frequency of a high frequency power supply 403 set at 100MHz. In Table 1, the high frequency power shows an effective powerobtained by subtracting a reflected power from an incident power. Acathode (high frequency electrode) 402 is an SUS cylinder having adiameter of 20 mm, of which outer face was covered with an alumina pipehaving an inner diameter of 21 mm and an outer diameter of 24 mm. Thealumina pipe was subjected to blast processing so that its surfaceroughness level was 20 μm in Rz with standard length of 2.5 mm. As forthe cylindrical substrate, six cylindrical substrates 405 were arrangedat equal intervals on the same circumference.

[0147] Also, a matching variable condenser 102 was variable in the 50 to1,000 pF range, and a tuning variable condenser 103 was variable in the5 to 250 pF range. The output of the high frequency power supply 403 was50 Ω, and was linked to the matching box 404 by a coaxial cable having acharacteristic impedance of 50 Ω.

[0148] The impedance variable ranges for the matching variable condenser102 and the tuning variable condenser 103 were first determined usingthis apparatus.

[0149] First, the cylindrical substrate 405 was installed on a rotationshaft 408 in a reactor container 401. Thereafter, gas in the reactorcontainer 401 was exhausted through an exhaust pipe 411 by an exhaustsystem (not shown). Subsequently, the cylindrical substrate 405 wasrotated at the speed of 10 rpm with a motor (not shown) via the rotationshaft 408, and 500 ml/min (normal) of argon (Ar) gas was supplied to thereactor container 401 from raw material gas supplying means 412 whilethe cylindrical substrate 405 was heated by a heating element 407 withcontrol being performed so that its temperature kept at 250° C. and thisstate was maintained for two hours.

[0150] Then, the supply of Ar gas was stopped, and gas in the reactorcontainer 401 was exhausted through the exhaust pipe 411 by the exhaustsystem (not shown), followed by introducing a raw material gas for usein formation of a charge injection blocking layer shown in Table 1 viathe raw material gas supplying means 412. After it was checked that theflow rate of raw material gas reached a preset flow rate, and thepressure in the reactor container 401 was stabilized, the output of thehigh frequency power supply 403 was set to a value equivalent to 20% ofthe condition of the charge injection blocking layer shown in Table 1.In this condition, the capacity of the matching variable condenser 102in the matching box 404 was adjusted so that the difference between anoutput voltage from an impedance detector 108 and a reference voltagewas reduced. The reference voltage was set to the value of outputvoltage from the impedance detector 108 with the impedance at the highfrequency power input point of the matching box 404 on the load sidebeing considered as 50 Ω. At the same time, the capacity of the tuningvariable condenser 103 in the matching box 404 was adjusted so that thedifference between an output voltage from a phase detector 107 and areference voltage was reduced. The reference voltage was set to thevalue of output voltage from the phase detector 107 with phasedifference between the incident power at the high frequency power inputpoint of the matching box 404 on the load side and the reflected powerbeing considered as 0 degree.

[0151] After the capacities of the matching variable condenser 102 andthe tuning variable condenser 103 were adjusted so that the differencebetween the output voltage from the impedance detector 108 and thereference voltage and the difference between the output voltage from thephase detector 107 and the reference voltage were minimized in this way,the output of the high frequency power supply 403 was increased to avalue equivalent to the condition of the charge injection blocking layershown in Table 1 to produce a discharge, and the capacity of eachvariable condenser at the time when the discharge was produced wasdetermined. Subsequently, the charge injection blocking layer wasformed. When the formation of the charge injection blocking layer wasstarted, the capacities of the matching variable condenser 102 and thetuning variable condenser 103 were adjusted again so that the absolutevalue of impedance at the input point of the matching box 404, and thephase difference between the incident voltage and the reflected voltageare minimized. This adjustment was carried out at intervals of twominutes during formation of the charge injection blocking layer, and thevariation ranges of capacities of the matching variable condenser 102and the tuning variable condenser 103 were determined.

[0152] When the formation of the charge injection blocking layer wascompleted, the output of high frequency power was stopped, plasmaprocessing conditions such as a gas type, gas flow rate, pressure andthe like were switched to conditions for formation of thephotoconductive layer shown in Table 1, and the capacities of thematching variable condenser 102 and the tuning variable condenser 103during production of discharge, and the variation ranges of capacitiesof the matching variable condenser 102 and the tuning variable condenser103 during formation of the photoconductive layer were determined in thesame manner as formation of the charge injection blocking layer.

[0153] Similarly, the capacities of the matching variable condenser 102and the tuning variable condenser 103 during production of discharge forthe surface layer, and the variation ranges of capacities of thematching variable condenser 102 and the tuning variable condenser 103during formation of the surface layer were determined.

[0154] This experiment was conducted ten times to determine thevariation ranges of capacities of the matching variable condenser 102and the tuning variable condenser 103 during production of discharge forthe charge injection-blocking layer, photoconductive layer and surfacelayer, and the variation ranges of capacities of the matching variablecondenser 102 and the tuning variable condenser 103 during formation ofthose layers were determined.

[0155] The results are shown in Table 2. Based on the results, thevariation ranges of capacities of the matching variable condenser 102and the tuning variable condenser 103 during production of discharge forthe charge injection blocking layer, photoconductive layer and surfacelayer and during formation of those layers were determined so that thetwo conditions of:

[0156] (1) the center of the capacity variable range is the center ofthe capacity variation in Table 2; and

[0157] (2) the capacity variable range is twice as wide as the capacityvariation range in Table 2, were satisfied, namely ranges as shown inTable 3 were determined TABLE 1 Charge Photo- Injection conductiveSurface Blocking Layer Layer Layer Type of Gas and Flow Rate SiH₄(ml/min (normal)) 300 600 5 H₂ (ml/min (normal)) 300 200 B₂H₆ (ppm)1,000 1.8 Relative to SiH₄ CH₄ (ml/min (normal)) 55 NO (ml/min (normal))15 Substrate Temperature (° C.) 270 270 250 Internal Pressure (Pa) 2.01.0 1.5 High Frequency Power (W) 800 2,000 600 Film Thickness (μm) 3 270.5

[0158] TABLE 2 Starting Forming Starting Forming Starting Forming of BLof of PCL of of SL of Discharge BL Discharge PCL Discharge SL MCCapacity 680-720 700-810 430-480 470-550 510-530 530-570 Variation Range(pF) TC Capacity 78-86 72-80  88-116 82-98  94-102  92-108 VariationRange (pF)

[0159] TABLE 3 Starting Forming Starting Forming Starting Forming of BLof of PCL of of SL of Discharge BL Discharge PCL Discharge SL MCCapacity 660-740 645-865 405-505 430-590 500-540 510-590 Variable Range(pF) TC Capacity 74-90 68-84  74-130  74-106  90-106  84-116 VariableRange (pF)

[0160] After the variable ranges of capacities of the matching variablecondenser 102 and the tuning variable condenser 103 were determined, tenlots of electrophotographic photosensitive members were fabricated inthe following way according to the conditions shown in Table 1.

[0161] First, the cylindrical substrate 405 was installed on a rotationshaft 408 in a reactor container 401 Thereafter, gas in the reactorcontainer 401 was exhausted through an exhaust pipe 411 by an exhaustsystem (not shown) Subsequently, the cylindrical substrate 405 wasrotated at the speed of 10 rpm with a motor (not shown) via the rotationshaft 408, and 500 ml/min (normal) of Ar gas was supplied to the reactorcontainer 401 from raw material gas supplying means 412 while thecylindrical substrate 405 was heated by a heating element 407 withcontrol being performed so that its temperature kept at 250° C. and thisstate was maintained for two hours.

[0162] Then, the supply of Ar gas was stopped, and gas in the reactorcontainer 401 was exhausted through the exhaust pipe 411 by the exhaustsystem (not shown), followed by introducing via the raw materialsupplying means 412 a raw material gas for use in formation of thecharge injection blocking layer shown in Table 1. After it was checkedthat the flow rate of raw material gas reached a preset flow rate, andthe pressure in the reactor container 401 was stabilized, the output ofthe high frequency power supply 403 was set to a value equivalent to 20%of the condition of the charge injection blocking layer shown inTable 1. In this state, the adjustment of capacities of the matchingcondenser 102 and the tuning condenser 103 was carried out within therange shown in Table 3. Specifically, at the inlet of the matchingcircuit 101, a high frequency current was detected by a currentdetection element 105, and a high frequency voltage was detected by avoltage detection element 106. The outputs of the current detectorelement 105 and the voltage detection element 106 were inputted to thephase difference detector 107 and the impedance detector 108 in thecontrol system 100. In the phase difference detector 107, the phase ofimpedance at the inlet of the matching circuit 101 was detected, and animpedance/phase control unit 109 was made to output a voltage consistentwith the phase of impedance. In the impedance/phase control unit 109,the impedance of the tuning variable condenser 103 was controlled basedon the voltage inputted from the phase difference detector 107 withinthe preset variable range at the time of the starting of discharge forthe charge injection blocking layer shown in Table 3. That is, thevoltage inputted from the phase difference detector 107 was comparedwith a reference voltage, and a voltage consistent with the differencetherebetween was supplied to a motor 110 for driving the tuning variablecondenser 103 to adjust the impedance so that the difference between thevoltage inputted from the phase difference detector 107 and thereference voltage was reduced. In this case, when the impedance of thetuning variable condenser 103 reached the maximum or minimum value inthe variable range at the time of the starting of discharge for thecharge injection blocking layer shown in Table 3, the supply of voltageto the motor 110 was immediately stopped to prevent the capacityvariable range shown in Table 3 from being exceeded. The referencevoltage was set to the value of output voltage from the phase detector107 with the phase difference between incident voltage and reflectedvoltage at the high frequency power input point of the matching box 404on the load side being considered as 0 degree.

[0163] On the other hand, in the impedance detector 108, the absolutevalue of impedance at the inlet of the matching circuit 101 wasdetected, the impedance/phase control unit 109 was made to output avoltage consistent with the absolute value of impedance. In theimpedance/phase control unit 109, the impedance of the matching variablecondenser 102 was controlled based on the voltage inputted from theimpedance detector 108 within the preset variable range at the time ofthe starting of discharge for the charge injection blocking layer shownin Table 3. That is, the voltage inputted from the impedance detector108 was compared with a reference voltage, and a voltage consistent withthe difference therebetween was supplied to a motor 112 for driving thematching variable condenser 102 to adjust the impedance so that thedifference between the voltage inputted from the impedance detector 108and the reference voltage was reduced. In this case, when the impedanceof the matching variable condenser 102 reached the maximum or minimumvalue in the variable range shown in Table 3. the supply of voltage tothe motor 112 was immediately stopped to prevent the capacity variablerange shown in Table 3 from being exceeded. The reference voltage wasset to the value of output voltage from the impedance detector 108 withthe impedance at the high frequency power input point of the matchingbox 404 on the load side being considered as 50 Ω.

[0164] In this way, the impedances of the matching variable condenser102 and the tuning variable condenser 103 were adjusted while the outputof the high frequency power supply 403 was increased to the value forthe charge injection blocking layer shown in Table 1, whereby adischarge was produced to start formation of the charge injectionblocking layer. When the formation of the charge injection blockinglayer was started, the set variable ranges of capacities of the matchingvariable condenser 102 and the tuning variable condenser 103 werechanged to the variable ranges to be applied during formation of thecharge injection blocking layer shown in Table 3. In the impedance/phasecontrol unit 109, the capacity of the tuning variable condenser 103 wasadjusted within the changed capacity variable range. A control methodwas employed in which when the capacity of the tuning variable condenser103 reaches the maximum or minimum value in the variable range, or thedifference between the voltage inputted from the phase detector 107 andthe reference voltage reached a level lower than or equal to thematching goal condition, the supply of voltage to the motor 110 isstopped. The reference voltage was set to the value of output voltagefrom the phase detector 107 with the phase difference between incidentvoltage and reflected voltage at the high frequency power input point ofthe matching box 404 on the load side being considered as 0 degree. Thematching goal condition was set such that the difference between thevoltage inputted from the phase detector 107 and the reference voltageis smaller than or equal to 5% of the reference voltage.

[0165] At the same time, in the impedance/phase control unit 109, thecapacity of the matching variable condenser 102 was adjusted within thechanged capacity variable range. A control method was employed in whichwhen the capacity of the matching variable condenser 102 reaches themaximum or minimum value in the variable range, or the differencebetween the voltage inputted from the impedance detector 108 and thereference voltage reached a level lower than or equal to the matchinggoal condition, the supply of voltage to the motor 112 is stopped. Thereference voltage was set to the value of output voltage from theimpedance detector 108 with the impedance at the high frequency powerinput point of the matching box 404 on the load side being considered as50 Ω. The matching goal condition was set such that the differencebetween the voltage inputted from the impedance detector 108 and thereference voltage is smaller than or equal to 5% of the referencevoltage.

[0166] After the formation of the charge injection blocking layer wascompleted in this way, the outputting of high frequency power wasstopped, plasma processing conditions such as the type of gas, the flowrate of gas and pressure were set to the conditions for formation of thephotoconductive layer shown in Table 1, and the set variable ranges ofcapacities of the matching variable condenser 102 and the tuningvariable condenser 103 were changed the ranges to be applied at the timeof starting discharge for the photoconductive layer shown in Table 3,followed by producing a discharge in the same way as the formation ofthe charge injection blocking layer to form the photoconductive layer.

[0167] After the formation of the photoconductive layer was completed,the outputting of high frequency power was stopped, plasma processingconditions such as the type of gas, the flow rate of gas and pressurewere set to the conditions for formation of the surface layer shown inTable 1, and the set variable ranges of capacities of the matchingvariable condenser 102 and the tuning variable condenser 103 werechanged the ranges to be applied at the time of starting discharge forthe surface layer shown in Table 3, followed by producing a discharge inthe same manner as the formation of the charge injection blocking layerto form the surface layer.

[0168] In this way, ten lots of electrophotographic photosensitivemembers (total 60 members) each constituted by a charge injectionblocking layer, a photoconductive layer and a surface layer werefabricated. The electrophotographic photosensitive member was formedstably in every lot.

Comparison Example 1

[0169] Ten lots of electrophotographic photosensitive members (total 60members) each constituted of a charge injection blocking layer, aphotoconductive layer and a surface layer were fabricated in the sanemanner as Example 1 except that the variable ranges of capacities of thematching variable condenser 102 and the tuning variable condenser 103were not set. As a result, the capacities of the matching variablecondenser 102 and the tuning variable condenser 103 were considerablydeviated from stable points temporarily to destabilize a dischargeduring formation of the electrophotographic photosensitive member inthree lots.

[0170] Amorphous silicon (a-Si) photosensitive members fabricated inthis way in Example 1 and Comparison example 1 were installed in acopier (NP-6750, manufactured by Canon Inc.) modified for proper testingto evaluate the characteristics of the photosensitive members.Evaluations were made for four items, namely “unevenness of imagedensity,” “photomemory,” “variation of properties” and “image defect”using the following specific evaluation methods.

[0171] Unevenness of Image Density

[0172] First, the current of a main electrifier was adjusted so that thevalue of dark area potential at the developer position was a constantvalue, and thereafter a given white paper with reflection density of 0.1or lower was used as an original to adjust the amount of image lightexposure so that the value of light area potential at the developerposition was a predetermined value. Then, a half tone chart manufacturedby Canon Inc. (part number: PY9-9042) was placed on a script pad, and anevaluation was made based on a difference between the maximum andminimum values of reflection density in the entire area of a copy imageobtained by coping. The average value for all photosensitive members wasused as the evaluation result. Thus, the smaller the value, the betterthe result is.

[0173] Photomemory

[0174] The current value of the main electrifier was adjusted so thatthe value dark area potential at the developer position was apredetermined value, and thereafter the amount of image light exposurewas adjusted so that the value of light area potential was apredetermined value using a given white paper as an original. In a copyimage obtained in such a manner that in this state, a ghost test chartmanufactured by Canon Inc. (part number: FY9-9040) having a black circlewith reflection density of 1.1 and a diameter of 5 mm attached theretowas placed on the script pad, and the half tone chart manufactured byCanon Inc. was superimposed thereon, a difference between the reflectiondensity of the black circle with a diameter of 5 mm of the ghost chartfound on the half tone copy and the reflection density of the half tonepart was determined to make an evaluation. Photomemory measurement wascarried out for the entire area in the bus line direction of thephotosensitive member (entire area along the longitudinal direction ofthe photosensitive member), and an evaluation was made based on adifference their maximum reflection densities. The average value for allphotosensitive members was used as the evaluation result. Thus, thesmaller the value, the better the result is.

[0175] Variation of Properties

[0176] Maximum and minimum values of the evaluation results for allphotosensitive members in the above “photomemory” evaluation weredetermined, and then the value of (maximum value)/(minimum value) wascalculated. Thus, the smaller the value, the smaller the variation ofproperties is, and thus the better the result is.

[0177] Image Defect

[0178] White dots with diameters of 0.1 mm or greater in the same areaof the copy image obtained by placing the half tone chart manufacturedby Canon Inc. (part number: FY9-9042) on the script pad to performcopying were counted, and an evaluation was made based on the countednumber. Thus, the smaller the value, the better the result is.

[0179] Results of evaluation are shown in Table 4. In Table 4, theevaluation results are based on those in Comparison Example 1. Theunevenness of image density is evaluated with reference to theevaluation results of Comparison Example 1 in accordance with thefollowing criteria: a symbol AA indicates an improvement to less than ¼in difference between maximum reflection densities; a symbol AA—Aindicates an improvement to ¼ or more and less than ½; a symbol Aindicates an improvement to ½ or more and less than ¾: a symbol A—BBindicates an improvement to ¾ or more; a symbol BB indicatesequivalence; and a symbol C indicates a degradation. In addition, the“variation of properties” was evaluated in accordance with the followingcriteria: a symbol AA indicates an improvement of 40% or more; a symbolA indicates an improvement of 20% or more and less than 40%; a symbol BBindicates an improvement of 10% or more and less than 20%; a symbol Bindicates an improvement of less than 10% or a deterioration of lessthan 10%; and a symbol C indicates a deterioration of 10% or more. Thephotomemory was evaluated in accordance with the following criteria: asymbol AA indicates an improvement to less than ¼ in difference betweenmaximum reflection densities; a symbol AA—A indicates an improvement to¼ or more and less than ½; a symbol A indicates an improvement to ½ ormore and less than ¾; a symbol A—BB indicates an improvement to ¾ ormore; a symbol BB indicates equivalence; and a symbol C indicates adegradation. The image defect was evaluated in accordance with thefollowing criteria: a symbol AA indicates an improvement to less than ¼in the number of white dots with diameters 0.1 mm or greater; a symbolAA—A indicates an improvement to ¼ or more and less than ½, a symbol Aindicates an improvement to ½ or more and less than ¾; a symbol A—BBindicates an improvement to ¾ or more; a symbol BB indicatesequivalence; and a symbol C indicates a degradation.

[0180] Electrophotographic photosensitive members fabricated in Example1 showed good results in all evaluation items to demonstrate the effectof the present invention. In addition, the electrophotographic imagesformed in Example 1 using the electrophotographic photosensitive membershad no image smears and were thus quite satisfactory. TABLE 4 Unevennessof Photo- Variation of Image Image Density memory Properties DefectExample 1 A-BB A-BB A A

Example 2

[0181] The deposition film forming apparatus and the matching box usedin Example 1 were used to determine matching goal conditions to beapplied during formation of the charge injection blocking layer,photoconductive layer and surface layer under the conditions shown inTable 1 according to the following procedure.

[0182] First, formation of the charge injection blocking layer wasstarted using a same procedure as used in determination of impedancevariable ranges in Example 1. When the formation of the charge injectionblocking layer was started, the capacities of the matching variablecondenser 102 and the tuning variable condenser 103 were changed within10% or smaller of power reflectivity while observing the incident powerand reflected power at the high frequency power input point of thematching box 404, and thereby the maximum value of difference betweenthe voltage outputted from the phase detector 107 and the phasereference voltage, and the maximum value of difference between thevoltage outputted from the impedance detector 108 and the impedancereference voltage were determined. Furthermore, the power reflectivityis a ratio of reflected power to the incident power. In addition, thephase reference voltage is set to the value of output voltage from thephase detector 107 with the phase difference between incident voltageand reflected voltage at the high frequency power input point of thematching box 404 on the load side being considered as 0 degree, whilethe impedance reference voltage was set to the value of output voltagefrom the impedance detector 108 with the impedance at the high frequencypower input point of the matching box 404 on the load side beingconsidered as 50 Ω.

[0183] This measurement of the maximum value of difference between thevoltage outputted from the phase detector 107 and the phase referencevoltage and the maximum value of difference between the voltageoutputted from the impedance detector 108 and the impedance referencevoltage was carried out during the formation of the charge injectionblocking layer at intervals of two minutes, and the largest maximumvalue among them was used to determine the phase matching goal conditionand the impedance matching goal condition described below.

Phase matching goal condition(%)={(maximum vale of difference betweenvoltage outputted from phase detector 107 and phase referencevoltage)/(phase reference voltage)}×100

Impedance matching goal condition(%)={(maximum value of differencebetween voltage outputted from impedance detector 108 and impedancereference voltage)/(impedance reference voltage)}×100

[0184] Similarly, the matching goal conditions applied during formationof the photoconductive layer and formation of the surface layer weredetermined. As a result, matching goal conditions as shown in Table 5were obtained for each layer. TABLE 5 Charge Photo- Injection conductiveSurface Blocking Layer Layer Layer Phase Matching Goal 4% 2% 5%Condition Impedance Matching 3% 2% 4% Goal Condition

[0185] After the matching goal conditions applied during formation ofeach layer were determined, ten lots of electrophotographicphotosensitive members (total 60 members) each constituted of a chargeinjection blocking layer, a photoconductive layer and a surface layerwere fabricated under the conditions shown in Table 1 in the same manneras Example 1. In this Example, however, the matching goal conditionswere set at the values shown in FIG. 5 for each of the charge injectionblocking layer, photoconductive layer and surface layer. That is, thematching goal condition was changed during formation of theelectrophotographic photosensitive member.

[0186] The electrophotographic photosensitive member was formed stablyin every lot.

Comparison Example 2

[0187] Ten lots of electrophotographic photosensitive members (total 60members) each constituted of a charge injection blocking layer, aphotoconductive layer and a surface layer were fabricated under theconditions shown in Table 1 in the same manner as Comparison Example 1except that both the phase matching goal condition and impedancematching goal condition were set at 2% as in the case of conditions forthe photoconductive layer in Example 2 in all the charge injectionblocking layer, photoconductive layer and surface layer.

[0188] As a result, the capacities of the matching variable condenser102 and the tuning variable condenser 103 were always varied in all thelots during formation of the surface layer, thus making it impossible toform the electrophotographic photosensitive member with stability.

[0189] The a-Si photosensitive members fabricated in this way in Example2 and Comparison Example 2 were installed in a copier (NP-6750,manufactured by Canon Inc.) modified for proper testing to evaluate thecharacteristics of the photosensitive members. Evaluations were made forfour items, namely “unevenness of image density,” “photomemory,”“variation of properties” and “image defect” using specific evaluationmethods same as those in Example 1.

[0190] Results of evaluation are shown in Table 6. Table 6 shows resultsof evaluation conducted in the same manner as Example 1 with referenceto the evaluation results of Comparison Example 1.

[0191] The electrophotographic photosensitive member fabricated inExample 2 showed good results in all the evaluation items to demonstratethe effect of the present invention. In addition, theelectrophotographic photosensitive member fabricated in Example 2 hadbetter properties than the electrophotographic photosensitive memberfabricated in Example 1. It has been shown by the comparison betweenExample 2 and Comparative Example 2 that this effect of Example 2 is dueto not just the fact that the matching goal condition was narrowedcompared to Example 1, but the fact that the impedance variable rangewas changed as plasma processing proceeded, and the matching goalcondition was also changed as plasma processing proceeded. TABLE 6Unevenness of Photo- Variation of Image Image Density memory PropertiesDefect Example 2 A A AA AA-A Comparison C C C C Example 2

Example 3

[0192] The deposition film forming apparatus shown in FIG. 2 was used toform a-Si photosensitive members under the conditions shown in Table 7.In FIGS. 2A and 2B, FIG. 2A is a schematic sectional view of thedeposition film forming apparatus, and FIG. 2B is a schematic sectionalview taken along the cutting plane line 2B-2B in FIG. 2A. An exhaustopening 209 is provided in the bottom of a reactor container 201, andthe other end of the exhaust opening 209 is connected to an exhaustsystem (not shown). Twelve cylindrical substrates 205 being aluminumcylinders with diameters of 30 mm and lengths of 358 mm on which adeposition film is to be formed are installed while being placed on aholder 206, in such a manner as to surround the central portion of thereactor container 201 and in parallel with one another. The cylindricalsubstrate 205 is supported on a rotation shaft) 208, and is heated by aheating element 207. A motor (not shown) is driven, whereby the rotationshaft 208 is rotated, and the cylindrical substrate 205 rotates aroundthe central axis in the bus line direction (central axis along thelength of the cylindrical substrate). The cylindrical substrate 205 iskept at a ground potential via the rotation shaft 208.

[0193] A raw material gas is supplied to the reactor container 201 fromraw material gas supplying means 210. The raw material gas supplyingmeans 210 is an alumina pipe with an inner diameter of 10 mm and anouter diameter of 13 mm, has its ends sealed, and is capable ofsupplying a raw material gas from a gas blast nozzle with a diameter of1.2 mm provided on the pipe. The raw material gas supplying means 210has its surface subjected to blast processing so that its surfaceroughness level is 20 μm in Rz with standard length of 2.5 mm.

[0194] Six rod-shaped high frequency electrodes 202 are placed inparallel with one another outside an alumina cylindrical dielectric wall203 constituting a part of the reactor container 201, and furtheroutside thereof, a high frequency power shield 204 is provided in such amanner as to cylindrically surround the cylindrical dielectric wall 203.

[0195] The frequency of a high frequency power supply 211 is 60 MHz, andthe high frequency power outputted from the high frequency power supply211 is supplied to the high frequency electrode 202 via a matching box212. The output impedance of the high frequency power supply 211 is 50Ω, and the high frequency power supply 211 and the matching box 212 areconnected together by a coaxial cable having a characteristic impedanceof 50 Ω. The high frequency electrode 202 is an SUS cylinder with adiameter of 20 mm. In addition, the alumina cylindrical dielectric wall203 constituting a part of the reactor container 201 has its innersurface subjected to blast processing so that its surface roughnesslevel is 20 μm in Rz with standard length of 2.5 mm. In addition, thematching box 212 has as its specific configuration a configuration shownin FIG. 1, and the matching variable condenser 102 is variable withinthe range of from 5 pF to 1,000 pF while the tuning variable condenser103 is variable within the range of from 5 pF to 250 pF.

[0196] Using this apparatus, impedance variable ranges were determinedin the same manner as Example 1 under the conditions shown in Table 7.Then, matching goal conditions were determined in the same manner asExample 2 under the conditions shown in Table 7. Furthermore, afterformation of a charge transport layer, the flow rate of gas wascontinuously changed in 5 minutes without stopping a discharge, andthereafter the power was changed in 5 minutes to form a next layer,namely a charge generation layer. In addition, after formation of thecharge generation layer, the flow rate of gas, the power and thepressure were continuously changed in 15 minutes without stopping thedischarge to form a next layer, namely a surface layer. In this way, theimpedance variable ranges and the matching goal conditions shown inTable 8 were determined. TABLE 7 Charge Charge Transport GenerationSurface Layer Layer Layer Type of Gas and Flow Rate SiH₄ (ml/min(normal)) 300 200 15 H₂ (ml/min (normal)) 450 800 B₂H₆ (ppm)   8→1.5 1.5Relative to SiH₄ CH₄ (ml/min (normal)) 300→0  200 Substrate Temperature(° C.) 250 250 250 Internal Pressure (Pa) 7→4 4 3 High Frequency Power(W) 1,200 800 400 Thickness (μm) 25 5 0.5

[0197] TABLE 8 Forming Porming of Forming Starting of Charge Charge ofof Transport Generation Surface Discharge Layer Change Area Layer ChangeArea Layer MC Capacity 890-910 740-870 Continuously 710-840 Continuously510-550 Variable Changed Changed Range (pF) TC Capacity 330-360 250-310Continuously 330-380 Continuously 400-500 Variable Changed Changed Range(pF) Phase matching 2% Continuously 3% Continuously 5% Goal ConditionChanged Changed Impedance 2% 2% 2% Continuously 4% Matching Goal ChangedCondition

[0198] These impedance variable ranges and matching goal conditions wereused to fabricate five lots of electrophotographic photosensitivemembers under the conditions shown in Table 7 according to the followinggeneral procedure.

[0199] First, the cylindrical substrate 205 being a cylindrical aluminumcylinder supported on the substrate holder 206 was placed on therotation shaft 208 in the reactor container 201. Thereafter, gas in thereactor container 201 was exhausted through the exhaust pipe 209 by theexhaust system (not shown) Subsequently, the cylindrical substrate 205was rotated at the speed of 10 rpm with a motor (not shown) via therotation shaft 208, and 500 ml/min (normal) of Ar gas was supplied tothe reactor container 201 from raw material gas supplying means 210while the cylindrical substrate 205 was heated by a heating element 207with control being performed so that its temperature was kept at 250° C.and this state was maintained for two hours.

[0200] Then, the supply of Ar gas was stopped, and gas in the reactorcontainer 201 was exhausted through the exhaust pipe 208 by the exhaustsystem (not shown), followed by introducing via the raw materialsupplying means 210 a material gas for use in formation of the chargetransport layer shown in Table 7. After it was checked that the flowrate of raw material gas reached a preset flow rate, and the pressure inthe reactor container 201 was stabilized, the output of the highfrequency power supply 211 was set to a value equivalent to 20% of thecondition of the charge transport layer shown in Table 7. In this state,the adjustment of capacities of the matching condenser 102 and thetuning condenser 103 was carried out within the range shown in Table 7.The specific control method was similar to that of Example 1.

[0201] In this way, the impedances of the matching variable condenser102 and the tuning variable condenser 103 were adjusted while the outputof the high frequency power supply 211 was increased to the value forthe charge transport layer shown in Table 7, whereby a discharge wasproduced to start formation of the charge transport layer. When theformation of the charge injection blocking layer was started, the setvariable ranges of capacities of the matching variable condenser 102 andthe tuning variable condenser 103 were changed to the variable ranges tobe applied during formation of the charge transport layer shown in Table8, and phase matching goal conditions and impedance matching goalconditions were set to the conditions for the charge transport layershown in Table 8 The specific method for adjusting the impedance duringformation of the charge transport layer was similar to that of Example1.

[0202] After the charge transport layer was formed in this way, the flowrate of gas was first changed continuously in 5 minutes without stoppingthe discharge and then the power was changed in 5 minutes, so that theconditions were changed to those for formation of the next layer, namelythe charge generation layer. At this time, the variable ranges ofcapacities of the matching variable condenser 102 and the tuningvariable condenser 103, the phase matching goal condition and theimpedance matching goal condition were continuously changed, so that theset values thereof were changed to the set values for the chargegeneration layer in Table 8 before the formation of the chargegeneration layer was started. Thereafter, the charge generation layerand then the surface layer were similarly formed while changing thevariable ranges of capacities of the matching variable condenser 102 andthe tuning variable condenser 103, the phase matching goal condition andthe impedance matching goal condition to form the electrophotographicphotosensitive member. Furthermore, after the charge generation layerwas formed, the flow rate of gas, the power, the pressure, the variableranges of capacities of the matching variable condenser 102 and thetuning variable condenser 103, the phase matching goal condition and theimpedance matching goal condition were changed in 15 minutes withoutstopping the discharge to form the next layer, namely the surface layer.

[0203] In this way, ten lots of electrophotographic photosensitivemembers (total 120 members) each constituted of a charge transportlayer, a charge generation layer and a surface layer were fabricated.The electrophotographic photosensitive member was formed stably in everylot.

Comparison Example 3

[0204] Ten lots of electrophotographic photosensitive members (total 120members) each constituted of a charge transport layer, a chargegeneration layer and a surface layer were fabricated in the same manneras Example 3 under the conditions shown in Table 7 except that thevariable ranges of capacities of the matching variable condenser 102 andthe tuning variable condenser 103 were not set, and the phase matchinggoal condition and the impedance matching goal condition were fixed at5% for all the layers. As a result, the capacities of the matchingvariable condenser 102 and the tuning variable condenser 103 weretemporarily deviated considerably from stable points to destabilize thedischarge during formation of the electrophotographic photosensitivemember in three lots.

[0205] The a-Si photosensitive members fabricated in this way in Example3 and Comparison example 3 were installed in a copier (NP-6030,manufactured by Canon Inc.) modified for proper testing to evaluate theproperties of the photosensitive members. Evaluations were made for fouritems, namely “unevenness of image density,” “photomemory,” “variationof properties” and “image defect” using the specific evaluation methodssimilar to those of Example 1.

[0206] Results of evaluation are shown in Table 9. In Table 9, theevaluation was made with reference to the evaluation results ofComparison Example 3.

[0207] The electrophotographic photosensitive member fabricated inExample 3 showed satisfactory results in all the evaluation items todemonstrate the effect of the present invention. TABLE 9 Unevenness ofPhoto- Variation of Image Image Density memory Properties Defect Example3 AA-A AA-A AA AA-A

Example 4

[0208] Using the plasma processing apparatus for formation ofelectrophotographic photosensitive members shown in FIG. 3, anelectrophotographic photosensitive member was first formed under theconditions shown in Table 10, and the formed electrophotographicphotosensitive member was then taken out of a reactor container,followed by cleaning the reactor container under the conditions shown inTable 12 with a dummy substrate placed in the reactor container. Theplasma processing apparatus for formation of electrophotographicphotosensitive members as shown in FIG. 3 has the followingconfiguration.

[0209] Cylindrical substrates 302, a substrate supporter 303 containinga heater for heating substrates, and a raw material gas introductionpipe 306 are placed in a reactor container 301, and a high frequencymatching box 312 connected to an RF power supply 313 capable ofoutputting a high frequency power of 13.56 MHz is connected to a cathode304 constituting a part of the reactor container 301. The cathode 304 isinsulated from a ground potential by an insulator 305, and is kept at aground potential through the substrate support 303, thus making itpossible to apply an RF voltage between itself and the cylindricalsubstrate 302 also serving as an anode. The matching box 312 has aninner configuration identical to that shown in FIG. 1, and the matchingvariable condenser 102 has a capacity variable in the range of from 50pF to 1,000 pF while the tuning variable condenser 103 has a capacityvariable in the range of from 5 pF to 250 pF.

[0210] The reactor container 301 is connected to an exhaust system (notshown) via an exhaust valve 308, and gas in the reactor container 301can be exhausted to reduce the pressure therein by opening the exhaustvalve 308. In addition, reference numeral 309 in FIG. 3 denotes a leakvalve, and by opening the leak valve 309, a leak gas such as air,nitrogen gas, Ar gas, He gas or the like can be introduced into thereactor container 301 to release the reactor container 301 under reducedpressure to the atmosphere. Helium gas was used as a leak gas in thisExample.

[0211] The raw material gas is introduced into the reactor container 301from the raw material gas introduction pipe 306 connected to rawmaterial gas pipeline 310, and the pressure in the reactor container canbe detected by a pressure gauge 307.

[0212] Using this apparatus, the proper impedance variable ranges forthe matching variable condenser 102 and the tuning variable condenser103 were first determined in accordance with the following procedure.

[0213] First, the cylindrical substrate 302 is placed in the reactorcontainer 301, and an exhaust system (not shown) was caused to exhaustgas in the reactor container 301 by opening the exhaust valve 308.Subsequently, 650 ml/min (normal) of Ar gas was supplied to the reactorcontainer 301 from the raw material gas introduction pipe 306, theopening of the exhaust valve 308 was adjusted to keep the pressure inthe reactor container 501 at 85 Pa, and the cylindrical substrate 302was heated by the heater for heating substrates contained in thesubstrate support 303 while control was performed so that thetemperature of the cylindrical substrate was kept at 260° C. and thisstate was maintained for 1.5 hours.

[0214] Then, the supply of Ar gas was stopped, and gas in the reactorcontainer 301 was exhausted by the exhaust system (not shown), followedby introducing a raw material gas for use in formation of the chargeinjection blocking layer shown in Table 10 via the raw materialintroduction pipe 306. After it was checked that the flow rate of rawmaterial gas reached a predetermined flow rate, and the pressure in thereactor container 301 was stabilized, the output of the RF power supply303 was set to a value equivalent to 20% of the condition for the chargeinjection blocking layer as shown in Table 10. In this state, thecapacity of the matching variable condenser 102 in the matching box 312was adjusted so that the difference between the output voltage from theimpedance detector 108 and a reference voltage was reduced. Thereference voltage was set to the value of output voltage from theimpedance detector 108 with the impedance at the high frequency powerinput point of the matching box 312 on the load side being considered as50 Ω. At the same time, the capacity of the tuning variable condenser103 in the matching box 312 was adjusted so that the difference betweenthe output voltage from the phase detector 107 and a reference voltagewas reduced. The reference voltage was set to the value of outputvoltage from the phase detector 107 with the phase difference betweenthe incident voltage at the high frequency power input point of thematching box 312 on the load side and the reflected voltage thereofbeing considered as 0 degree.

[0215] After the capacities of the matching variable condenser 102 andthe tuning variable condenser 103 were adjusted so that the differencebetween the output voltage from the impedance detector 108 and thereference voltage, and the difference between the output voltage fromthe phase detector 107 and the reference voltage were minimized in thisway, the output of the RF power supply 313 was increased to the valuefor the charge injection blocking layer shown in Table 10 to produce adischarge, and the capacities of respective variable condensers at thetime when the discharge was produced were determined. Subsequently, thecharge injection blocking layer was formed. When the formation of thecharge injection blocking layer was started, the capacities of thematching variable condenser 102 and the tuning variable condenser 103were adjusted again so that the absolute value of impedance at the inputpoint of the matching box 312, and the phase difference between theincident voltage and the reflected voltage are minimized. Thisadjustment was continuously carried out during the formation of thecharge injection blocking layer to determine the variation ranges ofcapacities of the matching variable condenser 102 and the tuningvariable condenser 103 during the formation of the charge injectionblocking layer.

[0216] When the formation of the charge injection blocking layer wascompleted, the output of high frequency voltage was stopped, plasmaprocessing conditions such as the type and flow rate of gas and thepressure were changed to the conditions for formation of thephotoconductive layer shown in Table 10, and the variation ranges ofcapacities of the matching variable condenser 102 and the tuningvariable condenser 103 at the time of producing a discharge, and thevariation ranges of capacities of the matching variable condenser 102and the tuning variable condenser 103 during formation of thephotoconductive layer were determined in the same manner as that at thetime of forming the charge injection blocking layer.

[0217] For the surface layer, the variation ranges of capacities of thematching variable condenser 102 and the tuning variable condenser 103during production of a discharge, and the variation ranges of capacitiesof the matching variable condenser 102 and the tuning variable condenser103 during formation of the surface layer were similarly determined.

[0218] This experiment was repeated five times to determine thevariation ranges of capacities of the matching variable condenser 102and the tuning variable condenser 103 during production of the dischargefor the charge injection blocking layer, photoconductive layer andsurface layer, and the variation ranges of capacities of the matchingvariable condenser 102 and the tuning variable condenser 103 duringformation of those layers, and based on the results thereof, thevariable ranges of capacities of the matching variable condenser 102 andthe tuning variable condenser 103 during production of the discharge forthe charge injection blocking layer, photoconductive layer and surfacelayer, and the variable ranges of capacities of the matching variablecondenser 102 and the tuning variable condenser 103 during formation ofthose layers were determined in the same manner as Example 1.

[0219] Then, phase matching goal conditions and impedance matching goalconditions were determined in the same manner as Example 2. At thistime, the procedure for operating the plasma processing apparatus forformation of electrophotographic photosensitive members can be the sameas the procedure used for determining the variable ranges of capacitiesof the matching variable condenser 102 and the tuning variable condenser103.

[0220] The variable ranges of capacities of the matching variablecondenser 102 and the tuning variable condenser 103, the phase matchinggoal conditions and the impedance matching goal conditions determined inthis way are shown in Table 11.

[0221] After the variable ranges of capacities of the matching variablecondenser 102 and the tuning variable condenser 103, the phase matchinggoal conditions and the impedance matching goal conditions weredetermined in this way, a-Si based photosensitive members were formedunder the conditions shown in Tables 10 and 11. When the formation ofthe a-Si based photosensitive member was completed, the reactorcontainer 301 was adequately purged with a helium gas, and thereafterthe leak valve 309 was opened with the exhaust valve 308 closed tointroduce He into the reactor container 301, thereby releasing thereactor container 301 to the atmosphere. Subsequently, the cylindricalsubstrate on which a deposition film was formed, namely the a-SI basedphotosensitive member was taken out from the reactor container 301, anda dummy cylinder was placed therein instead.

[0222] Then, the exhaust valve 308 was opened to exhaust gas in thereactor container 301 by the exhaust system (not shown), followed bysupplying gases for cleaning processing as shown in Table 12 to thereactor container 301 through the raw material gas introduction pipe306, adjusting the opening of the exhaust valve 308 to adjust thepressure in the reactor container 301.

[0223] When the adjustment of pressure was completed, the variableranges of capacities of the matching variable condenser 102 and thetuning variable condenser 103, the phase matching goal conditions andthe impedance matching goal conditions were determined in the same wayas done in the case of formation of photosensitive members 13. Theconditions determined are shown in Table 13.

[0224] After the condition for formation of the a-Si basedphotosensitive member and the condition for cleaning the reactorcontainer were determined in this way, these conditions were used tocarry out formation of the a-Si based photosensitive member andsubsequent cleaning of the reactor container was carried out in fivecycles. TABLE 10 Charge Photo- Injection conductive Surface BlockingLayer Layer Layer Type of Gas and Flow Rate SiH₄ (ml/min (normal)) 300100 10 H₂ (ml/min (normal)) 300 600 B₂H₆ (ppm) 3,000 0.5 Relative toSiH₄ CH₄ (ml/min (normal)) 600 NO (ml/min (normal)) 15 SubstrateTemperature (° C.) 260 260 260 Internal Pressure (Pa) 40 40 55 HighFrequency Power (W) 300 600 200 Film Thickness (μm) 3 27 0.5

[0225] TABLE 11 Starting Forming Starting Forming Starting Forming of BLof of PCL of of SL of Discharge BL Discharge PCL Discharge SL MCCapacity 360-440 345-565 360-440 355-585 600-640 610-690 Variation Range(pF) TC Capacity  94-110  88-104  94-110  88-106 110-126 104-136Variation Range (pF) Phase Matching 5% 4% 6% Goal Condition Impedance 4%4% 6% Matching Goal Condition

[0226] TABLE 12 Cleaning Type of Gas and Flow Rate ClF₃ (ml/min(normal)) 200 Ar (ml/min (normal)) 1,600 Internal Pressure (Pa) 80 HighFrequency Power (W) 1,200 Time (minutes) 210

[0227] TABLE 13 Starting Start 60 min. 120 min. 180 min. of to to to toCleaning 60 min. 120 min. 180 min. 210 min. MC Cepacity 360-400 325-370325-365 320-365 300-340 Variation Range (pF) TC Capacity 130-145 122-138120-138 118-136 110-126 Variation Range (pF) Phase Matching 5% 5% 4% 3%Goal Condition Impedance 4% 4% 4% 3% Matching Goal Condition

Comparison Example 4

[0228] In the same manner as Example 4, a-Si based photosensitivemembers were formed under the conditions shown in Table 10 except thatthe variable ranges of capacities of the matching variable condenser 102and the tuning variable condenser 103 were not set, and the phasematching goal condition and the impedance matching goal condition werealways fixed at 6%. Furthermore, when the phase matching goal conditionand impedance matching goal condition were set at 4% as in the case ofPCL conditions in Example 4, the capacities of the matching variablecondenser 102 and the tuning variable condenser 103 were changed duringformation of the surface layer.

[0229] Then, cleaning of the reactor container was carried out in thesame manner as Example 4 except that the variable ranges of capacitiesof the matching variable condenser 102 and the tuning variable condenser103 were not set, and that the phase matching goal condition was fixedat 5% throughout the cleaning, and the impedance matching goal conditionwas fixed at 4% throughout the cleaning.

[0230] In this way, formation of the a-Si based photosensitive memberand subsequent cleaning of the reactor container were carried out infive cycles.

[0231] The a-Si based photosensitive members fabricated in this way inExample 4 and Comparison Example 4 were installed in a copier (NP-6750,manufactured by Canon Inc.) modified for proper testing to evaluate theproperties of the photosensitive members. Evaluations were made for fouritems, namely “unevenness of image density,” “photomemory,” “variationof properties” and “image defect” using the evaluation methods similarto those of Example 1.

[0232] Results of evaluation are shown in Table 14. In Table 14, theevaluation was made with reference to the evaluation results ofComparison Example 4.

[0233] The electrophotographic photosensitive member fabricated inExample 4 showed satisfactory results in all the evaluation items todemonstrate the effect of the present invention.

[0234] In addition, in Example 4, the reactor container was adequatelycleaned with no residues existing therein in any cycles, while inComparison Example 4, polysilane remained partially in the reactorcontainer in two of five cycles and therefore it was necessary to cleanthe reactor container again. TABLE 14 Unevenness of Photo- Variation ofImage Image Density memory Properties Defect Example 4 AA-A AA-A AA AA

Example 5

[0235] Using the plasma processing apparatus shown in FIGS. 6A and 6Band a matching box having the configuration shown in FIG. 1, ten lots ofa-Si based photosensitive members (total 60 members) each constituted ofa charge injection blocking layer, a photoconductive layer and a surfacelayer were fabricated on a cylindrical aluminum cylinder 605 with adiameter of 80 mm and a length of 358 mm under the conditions shown inTable 15, with oscillation frequencies of high frequency power supplies603 and 615 each fixed at 100 MHz. In Table 15, the high frequency powerrefers to effective power obtained by subtracting a reflected power froman incident power. High frequency electrodes 602 and 614 were SUScylinders with diameters of 20 mm, of which outer faces were coveredwith alumina pipes with inner diameters of 21 mm and outer diameters of24 mm. The alumina pipe was subjected to blast processing so that itssurface roughness level was 20 μm in Rz with reference length of 2.5 mm.Six cylindrical substrates 605 were arranged at equal intervals on thesame circumference.

[0236] In addition, as matching variable condensers 102 a and 102 b,those having capacities variable within the range of from 50 pF to 1,000pF inclusive were used, and as tuning variable condensers 103 a and 103b, those having capacities variable within the range of from 5 pF to 250pF inclusive. High frequency power supplies 603 and 615, of which outputimpedances were 50 Ω, were electrically connected to matching boxes 604and 616, respectively, via a coaxial cable having a characteristicimpedance of 50 Ω.

[0237] By plasma processing apparatus having a configuration describedabove, the impedance variable ranges for the matching variable condenser102 a and 102 b and the tuning variable condensers 103 a and 103 b werefirst determined according to the following procedure.

[0238] First, the cylindrical substrate 605 was placed on a rotationshaft 608 in the reactor container 601. Thereafter, gas in the reactorcontainer 601 was exhausted through an exhaust pipe 611 by an exhaustsystem (not shown). Subsequently, the cylindrical substrate 605 wasrotated with a motor (not shown) at a speed of 10 rpm via the rotationshaft 608, and 500 ml/min (normal) of Ar gas was supplied to the reactorcontainer 601 through a raw material gas supply pipe 612 while thecylindrical substrate 605 was heated by a heating element 607 withcontrol being performed so that the cylindrical substrate 605 was keptat a temperature of 250° C. and this state was maintained for two hours.

[0239] Then, the supply of Ar gas was stopped, and gas in the reactorcontainer 601 was exhausted through the exhaust pipe 611 by the exhaustsystem (not shown), followed by introducing a raw material gas for usein formation of the charge injection blocking layer shown in Table 15through the raw material gas supply pipe 612. After it was checked thatthe flow rate of raw material gas reached a predetermined flow rate, andthe pressure in the reactor container 601 was stabilized, the outputs ofthe high frequency power supplies 603 and 615 were set to a valueequivalent to 20% of the condition for the charge injection blockinglayer shown in Table 15. In this state, the capacities of the matchingvariable condensers 102 a and 102 b in the matching boxes 604 and 616were adjusted so that differences between output voltages from theimpedance detectors 108 a and 108 b and a reference voltage werereduced. The reference voltage was set to the values of output voltagesfrom the impedance detectors 108 a and 108 b with the impedance at thehigh frequency power input point of the matching boxes 604 and 616 onthe load side being considered as 50 Ω. At the same time, the capacitiesof the tuning variable condensers 103 a and 103 b in the matching boxes604 and 616 were adjusted so that differences between output voltagesfrom the phase detectors 107 a and 107 b and reference voltages werereduced. The reference voltage was set to values of output voltages fromthe phase detectors 107 a and 107 b with phase differences betweenincident voltages at the high frequency power input points of thematching boxes 604 and 616 on the load side and reflected voltagesthereof being considered as 0 degree.

[0240] After the capacities of the matching variable condensers 102 aand 102 b and the tuning variable condensers 103 a and 103 b wereadjusted so that the differences between the output voltages from theimpedance detectors 108 a and 108 b and the reference voltage, and thedifferences between the output voltages from the phase detectors 107 aand 107 b and the reference voltage were minimized in this way, theoutputs of the high frequency power supplies 603 and 615 were increasedto the values for the charge injection blocking layer conditions shownin Table 15 to produce a discharge, and the capacities of respectivevariable condensers at the time when the discharge was produced weredetermined. Subsequently, the charge injection blocking layer wasformed. After the formation of the charge injection blocking layer wasstarted, the capacities of the matching variable condensers 102 a and102 b and the tuning variable condensers 103 a and 103 b were adjustedagain so that the absolute values of impedance at the input points ofthe matching boxes 604 and 616, and the phase difference between theincident voltage and the reflected voltage were minimized. Thisadjustment was carried out at two-minute intervals during the formationof the charge injection blocking layer to determine the variation rangesof capacities of the matching variable condensers 102 a and 102 b andthe tuning variable condensers 103 a and 103 b during the formation ofthe charge injection blocking layer.

[0241] After the formation of the charge injection blocking layer wascompleted, the output of high frequency voltage was stopped, plasmaprocessing conditions such as the type and flow rate of gas and thepressure were changed to the conditions for formation of thephotoconductive layer shown in Table 15, and the variation ranges ofcapacities of the matching variable condensers 102 a and 102 b and thetuning variable condensers 103 a and 103 b during production of adischarge, and the variation ranges of capacities of the matchingvariable condensers 102 a and 102 b and the tuning-variable condenser103 a and 103 b during formation of the photoconductive layer weredetermined in the same way as done in the case of formation of thecharge injection blocking layer.

[0242] For the surface layer, the variation ranges of capacities of thematching variable condensers 102 a and 102 b and the tuning variablecondensers 103 a and 103 b during production of a discharge, and thevariation ranges of capacities of the matching variable condensers 102 aand 102 b and the tuning variable condensers 103 a and 103 b duringformation of the surface layer were similarly determined.

[0243] This experiment was repeated ten times to determine the variationranges of capacities of the matching variable condensers 102 a and 102 band the tuning variable condensers 103 a and 103 b during production ofthe discharge for the charge injection blocking layer, photoconductivelayer and surface layer, and the variation ranges of capacities of thematching variable condensers 102 a and 102 b and the tuning variablecondensers 103 a and 103 b during formation of those layers.

[0244] Based on the results, the variation ranges of capacities of thematching variable condensers 102 a and 102 b and the tuning variablecondensers 103 a and 103 b at the time of starting production of adischarge for the charge injection blocking layer, during formation ofthe charge injection blocking layer, at the time of starting productionof a discharge for the photoconductive layer, during formation of thephotoconductive layer, at the time of starting production of a dischargefor the surface layer and during formation of the surface layer weredetermined so as to meet the two conditions of:

[0245] (1) the center of the capacity variable range is the center ofthe capacity variation range; and

[0246] (2) the capacity variable range is twice as wide as the capacityvariation range. TABLE 15 Charge Photo- Injection conductive SurfaceBlocking Layer Layer Layer Type of Gas and Flow Rate SiH₄ (ml/min(normal)) 300 600 5 H₂ (ml/min (normal)) 300 200 B₂H₆ (ppm) 1,000 1.8Relative to SiH₄ CH₄ (ml/min (normal)) 55 NO (ml/min (normal)) 15Substrate Temperature (° C.) 270 270 250 Internal Pressure (Pa) 2.0 1.01.5 High Frequency Power (W) 200 500 150 (High Frequency Power Supply404) High Frequency Power (W) 200 1,500 450 Film (High Frequency PowerSupply 415) Thickness (μm) 3 27 0.5

[0247] After the variable ranges of capacities of the matching variablecondensers 102 a and 102 b and the tuning variable condensers 103 a and103 b were determined in this way, ten lots of electrophotographicphotosensitive members were fabricated in the following manner under theconditions shown in Table 15.

[0248] First, the cylindrical substrate 605 was placed on the rotationshaft 608 in the reactor container 601. Thereafter, gas in the reactorcontainer 601 was exhausted via the exhaust pipe 611 by the exhaustsystem (not shown). Subsequently, the cylindrical substrate 605 wasrotated with the motor (not shown) at a speed of 10 rpm via the rotationshaft 608, and 500 ml/min (normal) of Ar gas was supplied to the reactorcontainer 601 through the raw material gas supply pipe 612 while thecylindrical substrate 605 was heated by the heating element 607 withcontrol being performed so that the cylindrical substrate 605 was keptat a temperature of 250° C. and this state was maintained for two hours.

[0249] Then, the supply of Ar gas was stopped, and gas in the reactorcontainer 601 was exhausted through the exhaust pipe 611 by the exhaustsystem (not shown), followed by introducing a raw material gas for usein formation of the charge injection blocking layer shown in Table 15through the raw material gas supply pipe 612. After it was checked thatthe flow rate of raw material gas reached a predetermined flow rate, andthe pressure in the reactor container 601 was stabilized, the outputs ofthe high frequency power supplies 603 and 615 were set to a valueequivalent to 20% of the condition for the charge injection blockinglayer shown in Table 15.

[0250] Furthermore, the variable ranges of capacities at the startingproduction of a discharge for the charge injection blocking layer,during formation of the charge injection blocking layer, duringformation of photoconductive layer and during formation of the surfacelayer are previously inputted and set in impedance/phase control units109 a and 109 b based on the results of experiments for determiningvariable ranges of capacities, and a capacity variable range indicatingsignal is inputted therein to select desired variable ranges ofcapacities.

[0251] In this state, the capacity variable range indicating signal isfirst inputted in the impedance/phase control units 109 a and 109 b toselect the variable range of capacity at the time of starting productionof a discharge for the charge injection blocking layer, followed bystarting the automatic control of impedance. Specifically, at the inletsof matching circuits 111 a and 111 b, high frequency currents aredetected by current detection elements 105 a and 105 b, and highfrequency voltages are detected by voltage detection elements 106 a and106 b. The outputs of the current detection elements 105 a and 105 b,and the voltage detection elements 106 a and 106 b are inputted to phasedifference detectors 107 a and 107 b and impedance detectors 108 a and108 b in control systems 100 a and 100 b, respectively. The phasedifference detectors 107 a and 107 b detect phases of impedances at theinlets of the matching circuits 101 a and 101 b, and output voltagesconsistent with the phase of impedance to the impedance/phase controlunits 109 a and 109 b. The impedance/phase control units 109 a and 109 bcontrol the impedances of the tuning variable condensers 103 a and 103 bbased on the voltages inputted from the phase difference detectors 107 aand 107 b within a predetermined variable range at the time of startingproduction of a discharge for the charge injection blocking layer. Thatis, the voltages inputted from the phase difference detectors 107 a and107 b are compared with reference voltages, voltages consistent with thedifferences therebetween are supplied to motors 110 a and 110 b fordriving the tuning variable condensers 103 a and 103 b, and adjustmentsare made so that differences between the voltages inputted from thephase difference detectors 17 a and 17 b and the reference voltage arereduced. At this time, when the impedances of the tuning variablecondensers 103 a and 103 b reach maximum or minimum values in thevariable range at the time of starting production of a discharge for thecharge injection blocking layer, the supply of voltages to the motors110 a and 110 b. Is immediately stopped, and control is performed sothat the variable range of capacities is not exceeded. The referencevoltage is set to the values of output voltages from the phase detectors107 a and 107 b with the phase difference between the incident voltageat high frequency power input points of the matching boxes 604 and 616on the load sides and the reflected voltages thereof being considered as0 degree.

[0252] On the other hand, the impedance detectors 108 a and 108 b detectthe absolute values of impedance at the inlets of the matching circuits101 a and 101 b, and output voltages consistent with the absolute valuesof impedance to the impedance/phase control units 109 a and 109 b. Theimpedance/phase control units 109 a and 109 b control the impedances ofthe matching variable condensers 102 a and 102 b based on the voltagesinputted from the impedance detectors 108 a and 108 b within apredetermined variable range at the time of starting production of adischarge for the charge injection blocking layer. That is, the voltagesinputted from the impedance detectors 108 a and 108 b are compared withthe reference voltage, voltages consistent with the differencestherebetween are supplied to motors 112 a and 112 b for driving thematching variable condensers 102 a and 102 b, and adjustments are madeso that differences between the voltages inputted from the impedancedetectors 108 a and 108 b and the reference voltage is reduced At thistime, when the impedances of the matching variable condensers 102 a and102 b reach maximum or minimum values in the variable range, the supplyof voltages to the motors 112 a and 112 b is immediately stopped, andautomatic control is performed so that the variable range of capacitiesis not exceeded. The reference voltage is set to values of outputvoltages from the impedance detectors 108 a and 108 b with impedances atthe high frequency power input points of the matching boxes 604 and 616on the load sides being considered as 50 Ω.

[0253] With the impedances of the matching variable condensers 102 a and102 b and the tuning variable condensers 103 a and 103 b being adjustedwith automatic control in this way, the outputs of the high frequencypower supplies 603 and 615 were increased to the values for the chargeinjection blocking layer shown in Table 15, thereby producing adischarge to start formation of the charge injection blocking layer.After the formation of the charge injection blocking layer was started,capacity variable range indicating signals were inputted to theimpedance/phase control units 109 a and 109 b, whereby variable rangesof capacities to be applied during formation of the charge injectionblocking layer were selected, and the variable ranges of capacities ofthe matching variable condensers 102 a and 102 b and the tuning variablecondensers 103 a and 103 b were changed to the ranges to be appliedduring formation of the charge injection blocking layer. Theimpedance/phase control units 109 a and 109 b adjust the capacities ofthe tuning variable condensers 103 a and 103 b within the changedcapacity variable ranges. When the capacities of the tuning variablecondensers 103 a and 103 b reach maximum or minimum values in thevariable range, or differences between voltages inputted from the phasedetectors 107 a and 107 b and a reference voltage reach a levelequivalent to the matching goal condition or lower, the supply ofvoltages to the motors 110 a and 110 b is stopped. The reference voltageis set to values of output voltages from the phase detectors 107 a and107 b with the phase difference between the incident voltage at highfrequency power input points of the matching boxes 604 and 616 on theload sides and the reflected voltages being considered as 0 degree. Thematching goal condition is set so that the differences between thevoltages inputted from the phase detectors 107 a and 107 b and thereference voltage equal 6% or smaller of the reference voltage.

[0254] At the same time, the impedance/phase control units 109 a and 109b adjust the capacities of the matching variable condensers 102 a and102 b within the changed capacity variable range. When the capacities ofthe matching variable condensers 102 a and 102 b reach maximum orminimum values in the variable range, or differences between voltagesinputted from the impedance detectors 108 a and 108 b and a referencevoltage reach a level equivalent to the matching goal condition orlower, the supply of voltages to the motors 112 a and 112 b is stopped.The reference voltage is set to values of output voltages from theimpedance detectors 108 a and 108 b with impedances at the highfrequency power input points of the matching boxes 604 and 616 on theload sides being considered as 50 Ω. The matching goal condition is setso that the differences between the voltages inputted from the impedancedetectors 108 a and 108 b and the reference voltage equal 6% or smallerof the reference voltage.

[0255] After the charge injection blocking layer was formed in this way,the output of high frequency powers was stopped, plasma processingconditions such as the type and flow rate of gas and the pressure wereset to the conditions for formation of the photoconductive layer shownin Table 15, and capacity variable range indicating signals wereinputted to the impedance/phase control units 109 a and 109 b to selecta capacity variable range to be applied at the time of startingproduction of a discharge for the photoconductive layer, followed byproducing a discharge in the same manner as the case of the chargeinjection blocking layer to form the photoconductive layer.

[0256] After the formation of the photoconductive layer was completed,the output of high frequency powers was stopped, plasma processingconditions such as the type and flow rate of gas and the pressure wereset to the conditions for formation of the surface layer shown in Table15, and capacity variable range indicating signals were inputted to theimpedance/phase control units 109 a and 109 b to select a capacityvariable range to be applied at the time of starting production of adischarge for the surface layer, followed by producing a discharge inthe same manner as the formation of the charge injection blocking layerto form the surface layer.

[0257] In this way, ten lots of electrophotographic photosensitivemembers (total 60 members) each constituted of a charge injectionblocking layer, a photoconductive layer and a surface layer werefabricated. The electrophotographic photosensitive member was formedwith stability in every lot.

Comparison Example 5

[0258] Ten lots of electrophotographic photosensitive members (total 60members) each constituted of a charge injection blocking layer, aphotoconductive layer and a surface layer were fabricated in the samemanner as Example 5 under the conditions shown in Table 15 except thatthe variable ranges of capacities of the matching variable condensers102 a and 102 b and the tuning variable condensers 103 a and 103 b werenot set. As a result, the capacities of the matching variable condensers102 a and 102 b and the tuning variable condensers 103 a and 103 b weretemporarily deviated considerably from stable points to destabilize thedischarge during formation of the electrophotographic photosensitivemember in two lots.

[0259] The a-Si photosensitive members fabricated in this way in Example5 and Comparison Example 5 were installed in a copier (NP-6750,manufactured by Canon Inc., modified for proper testing) to makeevaluations for four items, namely “unevenness of image density.”“photomemory,” “variation of properties” and “image defect” using theevaluation methods similar to those of Example 1.

[0260] Results of evaluation are shown in Table 16. The evaluation wasmade with reference to the evaluation results of Comparison Example 5.

[0261] The electrophotographic photosensitive member fabricated inExample 5 showed satisfactory results in all the evaluation items. Inaddition, the electrophotographic image formed using theelectrophotographic photosensitive member fabricated in Example 5 had noimage smears, etc., and was thus quite satisfactory. TABLE 16 Unevennessof Variation of Image Image Density Photomemory Properties DefectExample 5 A A A AA-A

Example 6

[0262] Using the plasma processing apparatus and matching boxes used inExample 5, matching goal conditions during formation of the chargeinjection blocking layer, photoconductive layer and surface layer weredetermined under the conditions shown in Table 15 in accordance with thefollowing procedure, with the oscillation frequencies of high frequencypower supplies 603 and 615 being fixed at 100 MHz.

[0263] First, formation of the charge injection blocking layer wasstarted in accordance with a procedure similar to the procedure usedwhen the impedance variable range was determined in Example 5. Afterformation of the charge injection blocking layer was started, thecapacities of the matching variable condensers 102 a and 102 b andtuning variable condensers 103 a and 103 b were changed within 10% orless of power reflectivity while observing the incident power andreflected power at the high frequency power input points of the matchingboxes 604 and 616, and thereby the maximum value of differences betweenvoltages outputted from the phase detectors 107 a and 107 b and a phasereference voltage, and the maximum value of differences between voltagesoutputted from impedance detectors 108 a and 108 b and an impedancereference voltage were determined Furthermore, the power reflectivity isa ratio of reflected power to the incident power. In addition, the phasereference voltage was set to values of output voltages from the phasedetectors 107 a and 107 b with the phase difference between the incidentvoltage at high frequency power input points of the matching boxes 604and 616 on the load sides and the reflected voltages being considered as0 degree. In addition, the impedance reference voltage was set to valuesof output voltages from the impedance detectors 108 a and 108 b withimpedances at the high frequency power input points of the matchingboxes 604 and 616 on the load sides being considered as 50 Ω.

[0264] The maximum value of differences between voltages outputted fromthe phase detectors 107 a and 107 b and a phase reference voltage, andthe maximum value of differences between voltages outputted from theimpedance detectors 108 a and 108 b and an impedance reference voltagewere determined at intervals of two minutes during formation of thecharge injection blocking layer, and the largest maximum value amongthem was used to determine the following phase matching goal conditionand impedance matching goal condition.

Phase matching goal condition(%)={(maximum value of differences betweenoutput voltages of phase detectors 107 a and 107 b and phase referencevoltage)/(phase reference voltage)}×100

Impedance matching goal condition(%){(maximum value of differencesbetween output voltages of impedance detectors 108 a and 108 b andimpedance reference voltage)/(impedance reference voltage)}×100

[0265] Matching goal conditions to be applied during formation of thephotoconductive layer and during formation of the surface layer weresimilarly determined. The resulting matching goal conditions forrespective layers are shown in Table 17. TABLE 17 Charge Photo-Injection conductive Surface Blocking Layer Layer Layer Phase MatchingGoal 5% 3% 6% Condition Impedance Matching 4% 3% 6% Goal Condition

[0266] After the matching goal conditions to be applied during formationof respective layers were determined in this way, ten lots ofelectrophotographic photosensitive members (total 60 members) eachconstituted of a charge injection blocking layer, a photoconductivelayer and a surface layer were fabricated in the same manner as Example5 under the conditions shown in Table 15. Furthermore, in this Example,the matching goal conditions were set to the values shown in Table 17for each of the charge injection blocking layer, photoconductive layerand surface layer. That is, the matching goal conditions were changedduring formation of the electrophotographic photosensitive member.

[0267] As a result, the electrophotographic photosensitive member wasformed with stability in every lot.

Comparison Example 6

[0268] Ten lots of electrophotographic photosensitive members (total 60members) each constituted of a charge injection blocking layer, aphotoconductive layer and a surface layer were fabricated in the samemanner as Comparison Example 5 under the conditions shown in Table 15except that the phase matching goal condition and the impedance matchinggoal condition were fixed at 3% as in the case of the condition for thephotoconductive layer in Example 6 in all of the charge injectionblocking layer, photoconductive layer and surface layer.

[0269] As a result, the capacities of the matching variable condensers102 a and 102 b and the tuning variable condensers 103 a and 103 b werealways fluctuated during formation of the surface layer, thus making itimpossible to form the electrophotographic photosensitive member withstability in all lots.

[0270] For the a-Si photosensitive members fabricated in this way inExample 6 and Comparison Example 6, evaluations were made for fouritems, namely “unevenness of image density,” “photomemory,” “variationof properties” and “image defect” using the evaluation methods similarto those of Example 1.

[0271] Results of evaluation are shown in Table 18. The evaluation wasmade with reference to the evaluation results of Example 1.

[0272] The electrophotographic photosensitive member fabricated inExample 6 showed satisfactory results in all the evaluation items. Inaddition, the electrophotographic photosensitive member fabricated inExample 6 had better properties than the electrophotographicphotosensitive member fabricated in Example 5. It has been shown fromcomparison with the results from Comparison Example 6 that this effectof Example 6 is due to not just the fact that the matching goalcondition was narrowed compared to Example 5, but the fact that theimpedance variable range was changed as plasma processing proceeded, andthe matching goal condition was also changed as plasma processingproceeded. TABLE 18 Unevenness of Photo- Variation of Image ImageDensity memory Properties Defect Example 6 AA-A A AA AA-A Comparative CC C C Example 6

Example 7

[0273] The plasma processing apparatus shown in FIGS. 7A and 7B was usedto form a-Si based photosensitive members under the conditions shown inTable 19. An aluminum cylinder with a diameter of 30 mm and a length of358 mm was used as a cylindrical substrate 705. A raw material gassupply pipe 710 was an alumina pipe with an inner diameter of 10 mm andan outer diameter of 13 mm, had its ends sealed, and was capable ofsupplying a raw material gas from a gas blast nozzle with a diameter of1.2 mm provided on the pipe. The raw material gas supply pipe 710 hadits surface subjected to blast processing so that its surface roughnesslevel was 20 μm in Rz with standard length of 2.5 mm.

[0274] A high frequency power supply 711 had a frequency of 120 MHz andan output impedance of 50 Ω. The high frequency power supply 711 and amatching box 712 were electrically connected together via a coaxialcable having a characteristic impedance of 50 Ω. In addition, a highfrequency power supply 713 had a frequency of 70 MHz and an outputimpedance of 50 Ω. The high frequency power supply 713 and a matchingbox 714 were electrically connected together via a coaxial cable havinga characteristic impedance of 50 Ω.

[0275] A high frequency electrode 702 was an SUS cylinder with adiameter of 20 mm. In addition, an alumina cylindrical dielectric wall703 constituting a part of a reactor container 701 had its inner surfacesubjected to blast processing so that the surface roughness level was 20μm in Rz with standard length of 2.5 mm.

[0276] In addition, specific configurations of the matching boxes 712and 714 are those shown in FIG. 1, but for discriminating betweenmembers in the matching box 712 and members in the matching box 714, themembers in the matching box 712 will be given a symbol “a” and themembers in the matching box 714 will be given a symbol “b” forconvenience in the description below.

[0277] Matching variable condensers 102 a and 102 b had capacitiesvariable in the range of from 50 pF to 1,000 pF inclusive, and tuningvariable condensers 103 a and 103 b had capacities variable in the rangeof from 5 pF to 250 pF inclusive.

[0278] Using the plasma processing apparatus having the configurationdescribed above, the impedance variable range was first determined inthe same manner as Example 5 under the conditions shown in Table 19.Then, the matching goal condition was determined in the same manner asExample 6 under the conditions shown in Table 19. Furthermore, after thecharge transport layer was formed, the flow rate of gas was firstchanged continuously in 5 minutes, and the power was then changed in 5minutes without stopping production of a discharge to form the nextlayer, namely the charge generation layer. In addition, after the chargegeneration layer was formed, the flow rate of gas, the power and thepressure were continuously changed in 15 minutes without stoppingproduction of a discharge to form the next layer, namely the surfacelayer. In this way, the impedance variable range and the matching goalcondition were determined. TABLE 19 Charge Charge Transport GenerationSurface Layer Layer Layer Type and Flow Rate of Gas SiH₄ (ml/min(normal)) 300 200 15 H₂ (ml/min (normal)) 450 800 B₂H₆ (ppm)   8→1.5 1.5Relative to SiH₄ CH₄ (ml/min (normal)) 300→0  200 Substrate Temperature(° C.) 250 250 250 Internal Pressure (Pa) 7→4 4 3 High Frequency Power(W) 900 600 300 (High Frequency Power Supply 711) High Frequency Power(W) 300 200 100 (High Frequency Power Supply 713) Film Thickness (μm) 25 5 0.5

[0279] TABLE 20 Forming Forming of Forming Starting of Charge Charge ofof Transport Generation Surface Discharge Layer Change Area Layer ChangeArea Layer Phase matching 4% Continuously 5% Continuously 7% GoalCondition Changed Changed Impedance 4% 4% 4% Continuously 6% MatchingGoal Changed Condition

[0280] Using the impedance variable range and the matching goalcondition determined in this way, ten lots of electrophotographicphotosensitive members were fabricated in accordance with the followinggeneral procedure under the conditions shown in Table 19.

[0281] First, a cylindrical aluminum cylinder 705 supported on asubstrate holder 706 was placed on a rotation shaft 708 in the reactorcontainer 701. Thereafter, gas in the reactor container 701 wasexhausted through the exhaust pipe 709 by the exhaust system (notshown). Subsequently, the cylindrical aluminum cylinder 705 was rotatedat the speed of 10 rpm with a motor (not shown) via the rotation shaft708, and 500 ml/min (normal) of Ar gas was supplied to the reactorcontainer 701 from a raw material gas supply pipe 510 while thecylindrical aluminum cylinder 705 was heated by a heating element 707with control being performed so that its temperature was kept at 250° C.and this state was maintained for two hours.

[0282] Then, the supply of Ar gas was stopped, and gas in the reactorcontainer 701 was exhausted through the exhaust pipe 708 by the exhaustsystem (not shown), followed by introducing via the raw material gassupply pipe 710 a raw material gas for use in formation of the chargetransport layer shown in Table 19. After it was checked that the flowrate of raw material gas reached a predetermined flow rate, and thepressure in the reactor container 701 was stabilized, the outputs of thehigh frequency power supplies 711 and 713 were set to a value equivalentto 20% of the condition for the charge transport layer shown in Table19.

[0283] In this state, capacity variable range indicating signals werefirst inputted to the impedance/phase control units 109 a and 109 b toselect the capacity variable range to be applied at the time of startingproduction of a discharge for the charge transport layer, and thenautomatic control of impedance was started. The specific control methodwas similar to that of Example 5.

[0284] The impedances of the matching variable condensers 102 a and 102b and the tuning variable condensers 103 a and 103 b were adjusted inthis way, and at the same time the outputs of the high frequency powersupplies 711 and 713 were increased to the values of conditions for thecharge transport layer shown in Table 19, whereby a discharge wasproduced to start formation of the charge transport layer. After theformation of the charge transport layer was started, capacity variablerange indicating signals were inputted to the impedance/phase controlunits 109 a and 109 b, whereby the capacity valuable range to be appliedduring formation of the charge transport layer was determined, and thephase matching goal condition and impedance matching goal condition wereset to predetermined conditions for the charge transport layer shown inTable 20. The specific method for adjusting impedances during formationof the charge transport layer was similar to that of Example 5.

[0285] After the formation of the charge transport layer was completedin this way, the flow rate of gas was first changed continuously in 5minutes, and then the power was changed in 5 minutes without stoppingthe discharge, so that the conditions were changed to those forformation of the next layer, namely the charge generation layer. At thistime, the variable ranges of capacities of the matching variablecondensers 102 a and 102 b and the tuning variable condensers 103 a and103 b, the phase matching goal condition and the impedance matching goalcondition were continuously changed, so that the set values thereof werechanged to the set values for the charge generation layer when theformation of the charge generation layer was started. Thereafter, thecharge generation layer and then the surface layer were similarly formedwhile changing the variable ranges of capacities of the matchingvariable condensers 102 a and 102 b and the tuning variable condensers103 a and 103 b, the phase matching goal condition and the impedancematching goal condition to form the electrophotographic photosensitivemember. Furthermore, after the charge generation layer was formed, theflow rate of gas, the power, the pressure, the variable ranges ofcapacities of the matching variable condensers 102 a and 102 b and thetuning variable condensers 103 a and 103 b, the phase matching goalcondition and the impedance matching goal condition were changed in 15minutes to form the next layer, namely the surface layer withoutstopping the discharge.

[0286] In this way, ten lots of electrophotographic photosensitivemembers (total 120 members) each constituted of a charge transportlayer, a charge generation layer and a surface layer were fabricated.The electrophotographic photosensitive member was formed stably in everylot.

Comparison Example 7

[0287] Ten lots of electrophotographic photosensitive members (total 120members) each constituted of a charge transport layer, a chargegeneration layer and a surface layer were fabricated in the same manneras Example 7 under the conditions shown in Table 19 except that thevariable ranges of capacities of the matching variable condensers 102 aand 102 b and the tuning variable condensers 103 a and 103 b were notset, and the phase matching goal condition and the impedance matchinggoal condition were fixed at 7% for all the layers. As a result, thecapacities of the matching variable condensers 102 a and 102 b and thetuning variable condensers 103 a and 103 b were temporarily deviatedconsiderably from stable points to destabilize the discharge duringformation of the electrophotographic photosensitive member in five lots.

[0288] The a-Si based photosensitive members fabricated in this way inExample 7 and Comparison example 7 were installed in a copier (NP-6030,manufactured by Canon Inc., modified for proper testing) to evaluate theproperties of the photosensitive members. Evaluations were made for fouritems, namely “unevenness of image density,” “photomemory,” “variationof properties” and “image defect.”

[0289] Results of evaluation are shown in Table 21. The evaluation wasmade in the same manner as Examples 5 and 6 with reference to theevaluation results of Comparison Example 7.

[0290] The electrophotographic photosensitive member fabricated inExample 7 showed satisfactory results in all the evaluation items. TABLE21 Unevenness of Photo- Variation of Image Image Density memoryProperties Defect Example 7 AA AA AA AA-A

[0291] As described above, according to the present invention, in aplasma processing method and a plasma processing apparatus forprocessing an object to be processed, which is placed in a reactorcontainer, by decomposing a raw material gas introduced into the reactorcontainer using a high frequency power outputted from a high powersupply and introduced into the reactor container via a matching deviceand an electrode, the adjustment of impedance by the matching deviceduring plasma processing is carried out within a predetermined impedancevariable range, and the impedance variable range is changed as plasmaprocessing proceeds, whereby the adjustment of impedance by the matchingdevice is accomplished properly and stably, thus making it possible toachieve the improvement of plasma processing characteristics, theimprovement of reproducibility of plasma processing characteristics andreduction in costs for plasma processing.

What is claimed is:
 1. A plasma processing method comprising introducinga high frequency power outputted from a high frequency power supply intoa reactor container via a matching device and an electrode, decomposinga raw material gas introduced into said reactor container by means ofthe high frequency power and processing an object to be processed whichis placed in the reactor container, wherein the adjustment of impedanceby said matching device during plasma processing is controlled within apredetermined impedance variable range, and the impedance variable rangeis changed as plasma processing proceeds.
 2. The plasma processingmethod according to claim 1, wherein the impedance variable range issubstantially continuously changed as plasma processing proceeds.
 3. Theplasma processing method according to claim 1, wherein the adjustment ofimpedance by said matching device is carried out with automatic control.4. The plasma processing method according to claim 3, wherein theautomatic control is accomplished by adjusting the impedance of thematching device so that preset matching goal conditions are satisfied,and the matching goal conditions are changed as plasma processingproceeds.
 5. The plasma processing method according to claim 4, whereinthe matching goal conditions are substantially continuously changed asplasma processing proceeds.
 6. The plasma processing method according toclaim 1, wherein the frequency of high frequency power is not lower than50 MHz, and not higher than 250 MHz.
 7. The plasma processing methodaccording to claim 1, wherein the plasma processing is performed bycontinuously carrying out a plurality of processes with differentconditions.
 8. The plasma processing method according to claim 1,wherein the object to be processed is moved or rotated at least duringone period in the plasma processing.
 9. The plasma processing methodaccording to claim 1, wherein the plasma processing is performed forforming an electrophotographic photosensitive member.
 10. A plasmaprocessing method comprising introducing high frequency powers into areactor container via electrodes from a plurality of power supplysystems having high frequency power supplies and matching devicescapable of changing impedances, decomposing a raw material gasintroduced into said reactor container by means of said high frequencypowers, and plasma processing a substrate to be processed which isplaced in said reactor container, wherein the adjustment of impedance byat least one matching device of said matching devices of said pluralityof power supply systems during plasma processing is carried out withautomatic control within a predetermined impedance variable range. 11.The plasma processing method according to claim 10, wherein theadjustment of impedance by said matching device during plasma processingis carried out with automatic control within said predetermined variablerange in all said matching devices.
 12. The plasma processing methodaccording to claim 10, wherein high frequency powers of differentfrequencies are supplied to said reactor container at the same time. 13.The plasma processing method according to claim 10, wherein a pluralityof high frequency powers are supplied to said reactor container from thesame said electrode at the same time.
 14. The plasma processing methodaccording to claim 12, wherein said plurality of power supply systemssupply two types of high frequency powers with frequencies of not lowerthan 10 MHz and not higher than 250 MHz respectively, and assuming that,of the two types of high frequency powers, the frequency of the highfrequency power having a higher frequency is represented by f₁, and thefrequency of the high frequency power having a lower frequency isrepresented by f₂, a frequency ratio between f₁ and f₂ satisfies thecondition of: 0.1≦f ₂ /f ₁≦0.9
 15. The plasma processing methodaccording to claim 14, wherein said two types of high frequency powerssatisfy the condition of: 0.5<f ₂ /f ₁≦0.9
 16. The plasma processingmethod according to claim 10, wherein said impedance variable range ischanged as plasma processing proceeds.
 17. The plasma processing methodaccording to claim 10, wherein said automatic control is accomplished byadjusting the impedance of said matching device so that the presetmatching goal conditions are satisfied, and changing said matching goalconditions as plasma processing proceeds.
 18. The plasma processingmethod according to claim 10, wherein at least one of said impedancevariable range and the preset matching goal conditions is continuouslychanged as said plasma processing proceeds.
 19. The plasma processingmethod according to claim 10, wherein said plasma processing isperformed by continuously carrying out a plurality of processes withdifferent conditions.
 20. The plasma processing method according toclaim 10, wherein said substrate to be processed is moved or rotated atleast during one period in said plasma processing.
 21. The plasmaprocessing method according to claim 10, wherein an electrophotographicphotosensitive member is formed by said plasma processing.
 22. A plasmaprocessing apparatus comprising a reactor container for plasmaprocessing a substrate to be processed, raw material gas supplying meansfor supplying a raw material gas to said reactor container, and aplurality of power supply systems for supplying high frequency powers tosaid reactor container, wherein said plurality of power supply systemshave matching circuits capable of changing impedances and controlsystems for controlling the impedances of said matching circuits, saidcontrol system being capable of storing a variable range setting valuefor limiting an impedance variable range.
 23. The plasma processingapparatus according to claim 22, wherein said control system can store aplurality of said variable range setting values.
 24. The plasmaprocessing apparatus according to claim 22, wherein said control systemcan store a matching goal condition for determining whether matching isobtained or not.
 25. The plasma processing apparatus according to claim24, wherein said control system can store a plurality of said matchinggoal conditions.
 26. The plasma processing method according to claim 1,wherein said changing of the impedance variable range as plasmaprocessing proceeds is performed for each of processes with differentplasma processing conditions.
 27. The plasma processing method accordingto claim 10, wherein said preset impedance variable range is changed foreach of processes with different plasma processing conditions.